Migrate dev/benchmarks/macrobenchmarks to null safety. (#85501)

dev/benchmarks/macrobenchmarks/lib/main.dart

@@ -31,7 +31,7 @@ const String kMacrobenchmarks = 'Macrobenchmarks';
 void main() => runApp(const MacrobenchmarksApp());
 
 class MacrobenchmarksApp extends StatelessWidget {
-  const MacrobenchmarksApp({Key key, this.initialRoute = '/'}) : super(key: key);
+  const MacrobenchmarksApp({Key? key, this.initialRoute = '/'}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -68,7 +68,7 @@ class MacrobenchmarksApp extends StatelessWidget {
 }
 
 class HomePage extends StatelessWidget {
-  const HomePage({Key key}) : super(key: key);
+  const HomePage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/animated_image.dart

@@ -5,9 +5,9 @@
 import 'package:flutter/material.dart';
 
 class AnimatedImagePage extends StatelessWidget {
-  const AnimatedImagePage({Key key, this.onFrame}) : super(key: key);
+  const AnimatedImagePage({Key? key, this.onFrame}) : super(key: key);
 
-  final ValueChanged<int> onFrame;
+  final ValueChanged<int>? onFrame;
 
   @override
   Widget build(BuildContext context) {
@@ -18,9 +18,9 @@ class AnimatedImagePage extends StatelessWidget {
       body: Image.asset(
         'animated_images/animated_flutter_lgtm.gif',
         package: 'flutter_gallery_assets',
-        frameBuilder: (BuildContext context, Widget child, int/*?*/ frame, bool syncCall) {
+        frameBuilder: (BuildContext context, Widget child, int? frame, bool syncCall) {
           if (onFrame != null && frame != null) {
-            onFrame(frame);
+            onFrame?.call(frame);
           }
           return child;
         },

dev/benchmarks/macrobenchmarks/lib/src/animated_placeholder.dart

@@ -24,7 +24,7 @@ const String kBlueSquare = 'iVBORw0KGgoAAAANSUhEUgAAADIAAAAyCAYAAAAeP4ixAAAASEl'
 /// A 10x10 grid of animated looping placeholder gifts that fade into a
 /// blue square.
 class AnimatedPlaceholderPage extends StatelessWidget {
-  const AnimatedPlaceholderPage({Key key}) : super(key: key);
+  const AnimatedPlaceholderPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/animation_with_microtasks.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class AnimationWithMicrotasks extends StatefulWidget {
-  const AnimationWithMicrotasks({Key key}) : super(key: key);
+  const AnimationWithMicrotasks({Key? key}) : super(key: key);
 
   @override
   State<AnimationWithMicrotasks> createState() => _AnimationWithMicrotasksState();

dev/benchmarks/macrobenchmarks/lib/src/backdrop_filter.dart

@@ -7,7 +7,7 @@ import 'dart:ui';
 import 'package:flutter/material.dart';
 
 class BackdropFilterPage extends StatefulWidget {
-  const BackdropFilterPage({Key key}) : super(key: key);
+  const BackdropFilterPage({Key? key}) : super(key: key);
 
   @override
   State<BackdropFilterPage> createState() => _BackdropFilterPageState();
@@ -16,7 +16,7 @@ class BackdropFilterPage extends StatefulWidget {
 class _BackdropFilterPageState extends State<BackdropFilterPage> with TickerProviderStateMixin {
   bool _blurGroup = false;
   bool _blurTexts = true;
-  AnimationController animation;
+  late AnimationController animation;
 
   @override
   void initState() {
@@ -77,7 +77,7 @@ class _BackdropFilterPageState extends State<BackdropFilterPage> with TickerProv
                     child: Center(
                       child: AnimatedBuilder(
                           animation: animation,
-                          builder: (BuildContext c, Widget w) {
+                          builder: (BuildContext c, Widget? w) {
                             final int val = (animation.value * 255).round();
                             return Container(
                                 width: 50,
@@ -99,13 +99,13 @@ class _BackdropFilterPageState extends State<BackdropFilterPage> with TickerProv
                     const Text('Backdrop per txt:'),
                     Checkbox(
                       value: _blurTexts,
-                      onChanged: (bool v) => setState(() { _blurTexts = v; }),
+                      onChanged: (bool? v) => setState(() { _blurTexts = v ?? false; }),
                     ),
                     const SizedBox(width: 10),
                     const Text('Backdrop grid:'),
                     Checkbox(
                       value: _blurGroup,
-                      onChanged: (bool v) => setState(() { _blurGroup = v; }),
+                      onChanged: (bool? v) => setState(() { _blurGroup = v ?? false; }),
                     ),
                   ],
                 ),

dev/benchmarks/macrobenchmarks/lib/src/color_filter_and_fade.dart

@@ -9,7 +9,7 @@ import 'package:flutter/material.dart';
 // This tests whether the Opacity layer raster cache works with color filters.
 // See https://github.com/flutter/flutter/issues/51975.
 class ColorFilterAndFadePage extends StatefulWidget {
-  const ColorFilterAndFadePage({Key key}) : super(key: key);
+  const ColorFilterAndFadePage({Key? key}) : super(key: key);
 
   @override
   State<ColorFilterAndFadePage> createState() => _ColorFilterAndFadePageState();
@@ -79,9 +79,9 @@ class _ColorFilterAndFadePageState extends State<ColorFilterAndFadePage> with Ti
                 const Text('Use Color Filter:'),
                 Checkbox(
                   value: _useColorFilter,
-                  onChanged: (bool value) {
+                  onChanged: (bool? value) {
                     setState(() {
-                      _useColorFilter = value;
+                      _useColorFilter = value ?? false;
                     });
                   },
                 ),
@@ -111,17 +111,23 @@ class _ColorFilterAndFadePageState extends State<ColorFilterAndFadePage> with Ti
     _initAnimation();
   }
 
-  AnimationController _controller;
-  Animation<double> _opacityAnimation;
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  late AnimationController _controller;
+  late Animation<double> _opacityAnimation;
   bool _useColorFilter = true;
 }
 
 class _ShadowWidget extends StatelessWidget {
   const _ShadowWidget({
-    @required this.width,
-    @required this.height,
-    @required this.useColorFilter,
-    @required this.shadow,
+    required this.width,
+    required this.height,
+    required this.useColorFilter,
+    required this.shadow,
   });
 
   final double width;
@@ -148,7 +154,7 @@ class _ShadowWidget extends StatelessWidget {
 }
 
 class _ShadowPainter extends CustomPainter {
-  const _ShadowPainter({this.useColorFilter, @required this.shadow});
+  const _ShadowPainter({required this.useColorFilter, required this.shadow});
 
   final bool useColorFilter;
   final Shadow shadow;

dev/benchmarks/macrobenchmarks/lib/src/cubic_bezier.dart

@@ -8,7 +8,7 @@ import 'package:flutter/material.dart';
 
 // Based on https://github.com/eseidelGoogle/bezier_perf/blob/master/lib/main.dart
 class CubicBezierPage extends StatelessWidget {
-  const CubicBezierPage({Key key}) : super(key: key);
+  const CubicBezierPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -24,7 +24,7 @@ class CubicBezierPage extends StatelessWidget {
 }
 
 class Bezier extends StatelessWidget {
-  const Bezier(this.color, this.scale, {Key key, this.blur = 0.0, this.delay = 0.0}) : super(key: key);
+  const Bezier(this.color, this.scale, {Key? key, this.blur = 0.0, this.delay = 0.0}) : super(key: key);
 
   final Color color;
   final double scale;
@@ -79,7 +79,7 @@ class Bezier extends StatelessWidget {
         BezierPainter(Colors.grey, 0.0, _getLogoPath(), false),
         size: const Size(100.0, 100.0),
       ),
-      AnimatedBezier(color, scale, blur: blur, delay: delay),
+      AnimatedBezier(color, scale, blur: blur),
     ]);
   }
 }
@@ -88,17 +88,16 @@ class PathDetail {
   PathDetail(this.path, {this.translate, this.rotation});
 
   Path path;
-  List<double> translate = <double>[];
-  double rotation;
+  List<double>? translate = <double>[];
+  double? rotation;
 }
 
 class AnimatedBezier extends StatefulWidget {
-  const AnimatedBezier(this.color, this.scale, {Key key, this.blur = 0.0, this.delay}) : super(key: key);
+  const AnimatedBezier(this.color, this.scale, {Key? key, this.blur = 0.0}) : super(key: key);
 
   final Color color;
   final double scale;
   final double blur;
-  final double delay;
 
   @override
   State createState() => AnimatedBezierState();
@@ -113,9 +112,8 @@ class Point {
 
 class AnimatedBezierState extends State<AnimatedBezier>
     with SingleTickerProviderStateMixin {
-  double scale;
-  AnimationController controller;
-  CurvedAnimation curve;
+  late AnimationController controller;
+  late CurvedAnimation curve;
   bool isPlaying = false;
   List<List<Point>> pointList = <List<Point>>[
     <Point>[],
@@ -365,11 +363,11 @@ class BezierPainter extends CustomPainter {
 
     for (int i = 0; i < path.length; i++) {
       if (path[i].translate != null) {
-        canvas.translate(path[i].translate[0], path[i].translate[1]);
+        canvas.translate(path[i].translate![0], path[i].translate![1]);
       }
 
       if (path[i].rotation != null) {
-        canvas.rotate(path[i].rotation);
+        canvas.rotate(path[i].rotation!);
       }
 
       if (blur > 0) {

dev/benchmarks/macrobenchmarks/lib/src/cull_opacity.dart

@@ -5,15 +5,15 @@
 import 'package:flutter/material.dart';
 
 class CullOpacityPage extends StatefulWidget {
-  const CullOpacityPage({Key key}) : super(key: key);
+  const CullOpacityPage({Key? key}) : super(key: key);
 
   @override
   State<StatefulWidget> createState() => _CullOpacityPageState();
 }
 
 class _CullOpacityPageState extends State<CullOpacityPage> with SingleTickerProviderStateMixin {
-  Animation<double> _offsetY;
-  AnimationController _controller;
+  late Animation<double> _offsetY;
+  late AnimationController _controller;
 
   @override
   void initState() {

dev/benchmarks/macrobenchmarks/lib/src/filtered_child_animation.dart

@@ -13,7 +13,7 @@ enum FilterType {
 
 class FilteredChildAnimationPage extends StatefulWidget {
   const FilteredChildAnimationPage(this.initialFilterType, {
-    Key key,
+    Key? key,
     this.initialComplexChild = true,
     this.initialUseRepaintBoundary = true,
   }) : super(key: key);
@@ -27,13 +27,13 @@ class FilteredChildAnimationPage extends StatefulWidget {
 }
 
 class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage> with SingleTickerProviderStateMixin {
-  AnimationController _controller;
+  late AnimationController _controller;
   final GlobalKey _childKey = GlobalKey(debugLabel: 'child to animate');
   Offset _childCenter = Offset.zero;
 
-  FilterType _filterType;
-  bool _complexChild;
-  bool _useRepaintBoundary;
+  FilterType? _filterType;
+  late bool _complexChild;
+  late bool _useRepaintBoundary;
 
   @override
   void initState() {
@@ -41,8 +41,8 @@ class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage>
     _filterType = widget.initialFilterType;
     _complexChild = widget.initialComplexChild;
     _useRepaintBoundary = widget.initialUseRepaintBoundary;
-    WidgetsBinding.instance.addPostFrameCallback((_) {
-      final RenderBox childBox = _childKey.currentContext.findRenderObject() as RenderBox;
+    WidgetsBinding.instance!.addPostFrameCallback((_) {
+      final RenderBox childBox = _childKey.currentContext!.findRenderObject()! as RenderBox;
       _childCenter = childBox.paintBounds.center;
     });
     _controller = AnimationController(vsync: this, duration: const Duration(seconds: 2));
@@ -102,22 +102,23 @@ class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage>
     );
   }
 
-  Widget _animate({Widget child, bool protectChild}) {
+  Widget _animate({required Widget child, required bool protectChild}) {
     if (_filterType == null) {
       _controller.reset();
       return child;
     }
+    final FilterType filterType = _filterType!;
     _controller.repeat();
-    Widget Function(BuildContext, Widget) builder;
-    switch (_filterType) {
+    Widget Function(BuildContext, Widget?) builder;
+    switch (filterType) {
       case FilterType.opacity:
-        builder = (BuildContext context, Widget child) => Opacity(
+        builder = (BuildContext context, Widget? child) => Opacity(
           opacity: (_controller.value * 2.0 - 1.0).abs(),
           child: child,
         );
         break;
       case FilterType.rotateTransform:
-        builder = (BuildContext context, Widget child) => Transform(
+        builder = (BuildContext context, Widget? child) => Transform(
           transform: Matrix4.rotationZ(_controller.value * 2.0 * pi),
           alignment: Alignment.center,
           filterQuality: FilterQuality.low,
@@ -125,7 +126,7 @@ class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage>
         );
         break;
       case FilterType.rotateFilter:
-        builder = (BuildContext context, Widget child) => ImageFiltered(
+        builder = (BuildContext context, Widget? child) => ImageFiltered(
           imageFilter: ImageFilter.matrix((
               Matrix4.identity()
                 ..translate(_childCenter.dx, _childCenter.dy)
@@ -176,17 +177,17 @@ class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage>
                 const Text('Opacity:'),
                 Checkbox(
                   value: _filterType == FilterType.opacity,
-                  onChanged: (bool b) => _setFilterType(FilterType.opacity, b),
+                  onChanged: (bool? b) => _setFilterType(FilterType.opacity, b ?? false),
                 ),
                 const Text('Tx Rotate:'),
                 Checkbox(
                   value: _filterType == FilterType.rotateTransform,
-                  onChanged: (bool b) => _setFilterType(FilterType.rotateTransform, b),
+                  onChanged: (bool? b) => _setFilterType(FilterType.rotateTransform, b ?? false),
                 ),
                 const Text('IF Rotate:'),
                 Checkbox(
                   value: _filterType == FilterType.rotateFilter,
-                  onChanged: (bool b) => _setFilterType(FilterType.rotateFilter, b),
+                  onChanged: (bool? b) => _setFilterType(FilterType.rotateFilter, b ?? false),
                 ),
               ],
             ),
@@ -196,12 +197,12 @@ class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage>
                 const Text('Complex child:'),
                 Checkbox(
                   value: _complexChild,
-                  onChanged: (bool b) => setState(() => _complexChild = b),
+                  onChanged: (bool? b) => setState(() => _complexChild = b ?? false),
                 ),
                 const Text('RPB on child:'),
                 Checkbox(
                   value: _useRepaintBoundary,
-                  onChanged: (bool b) => setState(() => _useRepaintBoundary = b),
+                  onChanged: (bool? b) => setState(() => _useRepaintBoundary = b ?? false),
                 ),
               ],
             ),

dev/benchmarks/macrobenchmarks/lib/src/fullscreen_textfield.dart

@@ -48,7 +48,7 @@ const String textLotsOfText = 'Lorem ipsum dolor sit amet, consectetur '
   '🦻 👃 🫀 🫁 🧠 🦷 🦴 👀 👁 👅 👄 💋 🩸';
 
 class TextFieldPage extends StatelessWidget {
-  const TextFieldPage({Key key}) : super(key: key);
+  const TextFieldPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/heavy_grid_view.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class HeavyGridViewPage extends StatelessWidget {
-  const HeavyGridViewPage({Key key}) : super(key: key);
+  const HeavyGridViewPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -21,7 +21,7 @@ class HeavyWidget extends StatelessWidget {
   HeavyWidget(this.index) : super(key: ValueKey<int>(index));
 
   final int index;
-  final List<int> _weight = List<int>.filled(1000000, null);
+  final List<int> _weight = List<int>.filled(1000000, 0);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/large_image_changer.dart

@@ -8,16 +8,16 @@ import 'package:flutter/material.dart';
 
 /// Displays a new (from image cache's perspective) large image every 500ms.
 class LargeImageChangerPage extends StatefulWidget {
-  const LargeImageChangerPage({Key key}) : super(key: key);
+  const LargeImageChangerPage({Key? key}) : super(key: key);
 
   @override
   State<LargeImageChangerPage> createState() => _LargeImageChangerState();
 }
 
 class _LargeImageChangerState extends State<LargeImageChangerPage> {
-  Timer _timer;
+  Timer? _timer;
   int imageIndex = 0;
-  ImageProvider currentImage;
+  late ImageProvider currentImage;
 
   @override
   void didChangeDependencies() {

dev/benchmarks/macrobenchmarks/lib/src/large_images.dart

@@ -7,11 +7,11 @@ import 'dart:typed_data';
 import 'package:flutter/material.dart';
 
 class LargeImagesPage extends StatelessWidget {
-  const LargeImagesPage({Key key}) : super(key: key);
+  const LargeImagesPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
-    final ImageCache imageCache = PaintingBinding.instance.imageCache;
+    final ImageCache imageCache = PaintingBinding.instance!.imageCache!;
     imageCache.maximumSize = 30;
     imageCache.maximumSizeBytes = 50 << 20;
     return GridView.builder(
@@ -36,7 +36,7 @@ class DummyImage extends StatelessWidget {
         // creating many copies of the image to trigger the memory issue.
         return snapshot.data == null
             ? Container()
-            : Image.memory(snapshot.data.buffer.asUint8List());
+            : Image.memory(snapshot.data!.buffer.asUint8List());
       },
     );
   }

dev/benchmarks/macrobenchmarks/lib/src/multi_widget_construction.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class MultiWidgetConstructTable extends StatefulWidget {
-  const MultiWidgetConstructTable(this.columnCount, this.rowCount, {Key key})
+  const MultiWidgetConstructTable(this.columnCount, this.rowCount, {Key? key})
       : super(key: key);
 
   final int columnCount;
@@ -24,7 +24,7 @@ class _MultiWidgetConstructTableState extends State<MultiWidgetConstructTable>
   ];
   int counter = 0;
 
-  AnimationController _controller;
+  late AnimationController _controller;
 
   @override
   void initState() {
@@ -53,9 +53,9 @@ class _MultiWidgetConstructTableState extends State<MultiWidgetConstructTable>
         final double height = MediaQuery.of(context).size.height / widget.rowCount;
         final double colorPosition = _controller.value;
         final int c1Position = colorPosition.floor();
-        final Color c1 = colorList[c1Position % colorList.length][900];
-        final Color c2 = colorList[(c1Position + 1) % colorList.length][900];
-        final Color baseColor = Color.lerp(c1, c2, colorPosition - c1Position);
+        final Color c1 = colorList[c1Position % colorList.length][900]!;
+        final Color c2 = colorList[(c1Position + 1) % colorList.length][900]!;
+        final Color baseColor = Color.lerp(c1, c2, colorPosition - c1Position)!;
         counter++;
         return Scaffold(
           body: Table(
@@ -82,7 +82,7 @@ class _MultiWidgetConstructTableState extends State<MultiWidgetConstructTable>
                             // This key forces rebuilding the element
                             key: ValueKey<int>(widgetCounter + label),
                             color: Color.lerp(
-                                Colors.white, baseColor, label / totalLength),
+                                Colors.white, baseColor, label / totalLength)!,
                             constraints: BoxConstraints.expand(height: height),
                             child: Text('${widgetCounter + label}'),
                           );
@@ -99,7 +99,7 @@ class _MultiWidgetConstructTableState extends State<MultiWidgetConstructTable>
 
 // This class is intended to break the original Widget tree
 class MyContainer extends StatelessWidget {
-  const MyContainer({this.color, this.child, this.constraints, Key key})
+  const MyContainer({required this.color, required this.child, required this.constraints, Key? key})
       : super(key: key);
   final Color color;
   final Widget child;

dev/benchmarks/macrobenchmarks/lib/src/picture_cache.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class PictureCachePage extends StatelessWidget {
-  const PictureCachePage({Key key}) : super(key: key);
+  const PictureCachePage({Key? key}) : super(key: key);
 
   static const List<String> kTabNames = <String>['1', '2', '3', '4', '5'];
 
@@ -45,7 +45,7 @@ class PictureCachePage extends StatelessWidget {
 }
 
 class ListItem extends StatelessWidget {
-  const ListItem({Key key, this.index})
+  const ListItem({Key? key, required this.index})
       : super(key: key);
 
   final int index;

dev/benchmarks/macrobenchmarks/lib/src/post_backdrop_filter.dart

@@ -7,7 +7,7 @@ import 'dart:ui';
 import 'package:flutter/material.dart';
 
 class PostBackdropFilterPage extends StatefulWidget {
-  const PostBackdropFilterPage({Key key}) : super(key: key);
+  const PostBackdropFilterPage({Key? key}) : super(key: key);
 
   @override
   State<PostBackdropFilterPage> createState() => _PostBackdropFilterPageState();
@@ -15,7 +15,7 @@ class PostBackdropFilterPage extends StatefulWidget {
 
 class _PostBackdropFilterPageState extends State<PostBackdropFilterPage> with TickerProviderStateMixin {
   bool _includeBackdropFilter = false;
-  AnimationController animation;
+  late AnimationController animation;
 
   @override
   void initState() {
@@ -63,7 +63,7 @@ class _PostBackdropFilterPageState extends State<PostBackdropFilterPage> with Ti
                     child: Center(
                       child: AnimatedBuilder(
                           animation: animation,
-                          builder: (BuildContext c, Widget w) {
+                          builder: (BuildContext c, Widget? w) {
                             final int val = (animation.value * 255).round();
                             return Container(
                                 width: 50,
@@ -83,7 +83,7 @@ class _PostBackdropFilterPageState extends State<PostBackdropFilterPage> with Ti
                       Checkbox(
                         key: const Key('bdf-checkbox'), // this key is used by the driver test
                         value: _includeBackdropFilter,
-                        onChanged: (bool v) => setState(() { _includeBackdropFilter = v; }),
+                        onChanged: (bool? v) => setState(() { _includeBackdropFilter = v ?? false; }),
                       ),
                       MaterialButton(
                         key: const Key('bdf-animate'), // this key is used by the driver test

dev/benchmarks/macrobenchmarks/lib/src/simple_animation.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class SimpleAnimationPage extends StatelessWidget {
-  const SimpleAnimationPage({Key key}) : super(key: key);
+  const SimpleAnimationPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/simple_scroll.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class SimpleScroll extends StatelessWidget {
-  const SimpleScroll({Key key}) : super(key: key);
+  const SimpleScroll({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/stack_size.dart

@@ -81,7 +81,7 @@ final GetStackPointerCallback getStackPointer = () {
 }();
 
 class StackSizePage extends StatelessWidget {
-  const StackSizePage({Key key}) : super(key: key);
+  const StackSizePage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -100,7 +100,7 @@ class StackSizePage extends StatelessWidget {
 }
 
 class ParentWidget extends StatelessWidget {
-  const ParentWidget({Key key}) : super(key: key);
+  const ParentWidget({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -110,7 +110,7 @@ class ParentWidget extends StatelessWidget {
 }
 
 class ChildWidget extends StatelessWidget {
-  const ChildWidget({this.parentStackSize, Key key}) : super(key: key);
+  const ChildWidget({required this.parentStackSize, Key? key}) : super(key: key);
   final int parentStackSize;
 
   @override

dev/benchmarks/macrobenchmarks/lib/src/text.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class TextPage extends StatelessWidget {
-  const TextPage({Key key}) : super(key: key);
+  const TextPage({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/web/bench_build_image.dart

@@ -52,7 +52,7 @@ class BenchBuildImage extends WidgetRecorder {
 }
 
 class _RotatingWidget extends StatefulWidget {
-  const _RotatingWidget({this.child, Key key}) : super(key: key);
+  const _RotatingWidget({required this.child, Key? key}) : super(key: key);
 
   final Widget child;
 
@@ -61,7 +61,7 @@ class _RotatingWidget extends StatefulWidget {
 }
 
 class _RotatingWidgetState extends State<_RotatingWidget> with SingleTickerProviderStateMixin {
-  AnimationController controller;
+  late AnimationController controller;
 
   @override
   void initState() {
@@ -72,11 +72,17 @@ class _RotatingWidgetState extends State<_RotatingWidget> with SingleTickerProvi
     )..repeat();
   }
 
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     return AnimatedBuilder(
       animation: controller,
-      builder: (BuildContext context, Widget child) {
+      builder: (BuildContext context, Widget? child) {
         return Transform(
           transform: Matrix4.identity()..rotateZ(2 * math.pi * controller.value),
           child: widget.child,
@@ -84,5 +90,4 @@ class _RotatingWidgetState extends State<_RotatingWidget> with SingleTickerProvi
       },
     );
   }
-
 }

dev/benchmarks/macrobenchmarks/lib/src/web/bench_build_material_checkbox.dart

@@ -14,7 +14,7 @@ class BenchBuildMaterialCheckbox extends WidgetBuildRecorder {
 
   static const String benchmarkName = 'build_material_checkbox';
 
-  static bool _isChecked;
+  static bool? _isChecked;
 
   @override
   Widget createWidget() {
@@ -33,7 +33,7 @@ class BenchBuildMaterialCheckbox extends WidgetBuildRecorder {
   Row _buildRow() {
     if (_isChecked == null) {
       _isChecked = true;
-    } else if (_isChecked) {
+    } else if (_isChecked!) {
       _isChecked = false;
     } else {
       _isChecked = null;
@@ -45,7 +45,7 @@ class BenchBuildMaterialCheckbox extends WidgetBuildRecorder {
           child: Checkbox(
             value: _isChecked,
             tristate: true,
-            onChanged: (bool newValue) {
+            onChanged: (bool? newValue) {
               // Intentionally empty.
             },
           ),

dev/benchmarks/macrobenchmarks/lib/src/web/bench_card_infinite_scroll.dart

@@ -35,7 +35,7 @@ class BenchCardInfiniteScroll extends WidgetRecorder {
 }
 
 class _InfiniteScrollCards extends StatefulWidget {
-  const _InfiniteScrollCards(this.initialOffset, this.finalOffset, {Key key}) : super(key: key);
+  const _InfiniteScrollCards(this.initialOffset, this.finalOffset, {Key? key}) : super(key: key);
 
   final double initialOffset;
   final double finalOffset;
@@ -47,8 +47,8 @@ class _InfiniteScrollCards extends StatefulWidget {
 class _InfiniteScrollCardsState extends State<_InfiniteScrollCards> {
   static const Duration stepDuration = Duration(seconds: 20);
 
-  ScrollController scrollController;
-  double offset;
+  late ScrollController scrollController;
+  late double offset;
 
   @override
   void initState() {
@@ -70,6 +70,12 @@ class _InfiniteScrollCardsState extends State<_InfiniteScrollCards> {
     });
   }
 
+  @override
+  void dispose() {
+    scrollController.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     return ListView.builder(

dev/benchmarks/macrobenchmarks/lib/src/web/bench_child_layers.dart

@@ -31,10 +31,10 @@ class BenchUpdateManyChildLayers extends SceneBuilderRecorder {
   /// is correctly pumping frames.
   double wobbleCounter = 0;
 
-  List<Picture> _pictures;
-  Size windowSize;
-  Size cellSize;
-  Size rectSize;
+  late List<Picture> _pictures;
+  late Size windowSize;
+  late Size cellSize;
+  late Size rectSize;
 
   @override
   Future<void> setUpAll() async {
@@ -55,7 +55,7 @@ class BenchUpdateManyChildLayers extends SceneBuilderRecorder {
     }
   }
 
-  OffsetEngineLayer _rootLayer;
+  OffsetEngineLayer? _rootLayer;
   final Map<int, OffsetEngineLayer> _layers = <int, OffsetEngineLayer>{};
 
   @override
@@ -64,7 +64,7 @@ class BenchUpdateManyChildLayers extends SceneBuilderRecorder {
     for (int row = 0; row < kRows; row++) {
       for (int col = 0; col < kColumns; col++) {
         final int layerId = 1000000 * row + col;
-        final OffsetEngineLayer oldLayer = _layers[layerId];
+        final OffsetEngineLayer? oldLayer = _layers[layerId];
         final double wobbleOffsetX = col * cellSize.width + (wobbleCounter - 5).abs();
         final double offsetY = row * cellSize.height;
         // Retain every other layer, so we exercise the update path 50% of the

dev/benchmarks/macrobenchmarks/lib/src/web/bench_dynamic_clip_on_static_picture.dart

@@ -93,9 +93,9 @@ class BenchDynamicClipOnStaticPicture extends SceneBuilderRecorder {
 
   static const String benchmarkName = 'dynamic_clip_on_static_picture';
 
-  Size screenSize;
-  Size clipSize;
-  Picture picture;
+  late Size screenSize;
+  late Size clipSize;
+  late Picture picture;
   double pictureVerticalOffset = 0.0;
 
   @override

dev/benchmarks/macrobenchmarks/lib/src/web/bench_mouse_region_grid_hover.dart

@@ -14,7 +14,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'recorder.dart';
 
 class _NestedMouseRegion extends StatelessWidget {
-  const _NestedMouseRegion({this.nests, this.child});
+  const _NestedMouseRegion({required this.nests, required this.child});
 
   final int nests;
   final Widget child;
@@ -42,10 +42,10 @@ class BenchMouseRegionGridHover extends WidgetRecorder {
 
   static const String benchmarkName = 'bench_mouse_region_grid_hover';
 
-  _Tester _tester;
+  late _Tester _tester;
 
   void handleDataPoint(Duration duration) {
-    profile.addDataPoint('hitTestDuration', duration, reported: true);
+    profile!.addDataPoint('hitTestDuration', duration, reported: true);
   }
 
   // Use a non-trivial border to force Web to switch painter
@@ -66,7 +66,7 @@ class BenchMouseRegionGridHover extends WidgetRecorder {
   void frameDidDraw() {
     if (!started) {
       started = true;
-      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) async {
+      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) async {
         _tester.start();
         registerDidStop(_tester.stop);
       });
@@ -119,22 +119,22 @@ class BenchMouseRegionGridHover extends WidgetRecorder {
 class _UntilNextFrame {
   _UntilNextFrame._();
 
-  static Completer<void> _completer;
+  static Completer<void>? _completer;
 
   static Future<void> wait() {
     if (_UntilNextFrame._completer == null) {
       _UntilNextFrame._completer = Completer<void>();
-      SchedulerBinding.instance.addPostFrameCallback((_) {
-        _UntilNextFrame._completer.complete(null);
+      SchedulerBinding.instance!.addPostFrameCallback((_) {
+        _UntilNextFrame._completer!.complete(null);
         _UntilNextFrame._completer = null;
       });
     }
-    return _UntilNextFrame._completer.future;
+    return _UntilNextFrame._completer!.future;
   }
 }
 
 class _Tester {
-  _Tester({this.onDataPoint});
+  _Tester({required this.onDataPoint});
 
   final ValueSetter<Duration> onDataPoint;
 
@@ -145,12 +145,12 @@ class _Tester {
   TestGesture get gesture {
     return _gesture ??= TestGesture(
       dispatcher: (PointerEvent event) async {
-        RendererBinding.instance.handlePointerEvent(event);
+        RendererBinding.instance!.handlePointerEvent(event);
       },
       kind: PointerDeviceKind.mouse,
     );
   }
-  TestGesture _gesture;
+  TestGesture? _gesture;
 
   Duration currentTime = Duration.zero;
 

dev/benchmarks/macrobenchmarks/lib/src/web/bench_mouse_region_grid_scroll.dart

@@ -41,7 +41,7 @@ class BenchMouseRegionGridScroll extends WidgetRecorder {
   void frameDidDraw() {
     if (!started) {
       started = true;
-      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) async {
+      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) async {
         _tester.start();
         registerDidStop(_tester.stop);
       });
@@ -91,17 +91,17 @@ class BenchMouseRegionGridScroll extends WidgetRecorder {
 class _UntilNextFrame {
   _UntilNextFrame._();
 
-  static Completer<void> _completer;
+  static Completer<void>? _completer;
 
   static Future<void> wait() {
     if (_UntilNextFrame._completer == null) {
       _UntilNextFrame._completer = Completer<void>();
-      SchedulerBinding.instance.addPostFrameCallback((_) {
-        _UntilNextFrame._completer.complete(null);
+      SchedulerBinding.instance!.addPostFrameCallback((_) {
+        _UntilNextFrame._completer!.complete(null);
         _UntilNextFrame._completer = null;
       });
     }
-    return _UntilNextFrame._completer.future;
+    return _UntilNextFrame._completer!.future;
   }
 }
 
@@ -117,12 +117,12 @@ class _Tester {
   TestGesture get gesture {
     return _gesture ??= TestGesture(
       dispatcher: (PointerEvent event) async {
-        RendererBinding.instance.handlePointerEvent(event);
+        RendererBinding.instance!.handlePointerEvent(event);
       },
       kind: PointerDeviceKind.mouse,
     );
   }
-  TestGesture _gesture;
+  TestGesture? _gesture;
 
   Duration currentTime = Duration.zero;
 

dev/benchmarks/macrobenchmarks/lib/src/web/bench_mouse_region_mixed_grid_hover.dart

@@ -14,7 +14,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'recorder.dart';
 
 class _NestedMouseRegion extends StatelessWidget {
-  const _NestedMouseRegion({this.nests, this.child});
+  const _NestedMouseRegion({required this.nests, required this.child});
 
   final int nests;
   final Widget child;
@@ -33,7 +33,7 @@ class _NestedMouseRegion extends StatelessWidget {
 }
 
 class _NestedListener extends StatelessWidget {
-  const _NestedListener({this.nests, this.child});
+  const _NestedListener({required this.nests, required this.child});
 
   final int nests;
   final Widget child;
@@ -61,10 +61,10 @@ class BenchMouseRegionMixedGridHover extends WidgetRecorder {
 
   static const String benchmarkName = 'bench_mouse_region_mixed_grid_hover';
 
-  _Tester _tester;
+  late _Tester _tester;
 
   void handleDataPoint(Duration duration) {
-    profile.addDataPoint('hitTestDuration', duration, reported: true);
+    profile!.addDataPoint('hitTestDuration', duration, reported: true);
   }
 
   // Use a non-trivial border to force Web to switch painter
@@ -85,7 +85,7 @@ class BenchMouseRegionMixedGridHover extends WidgetRecorder {
   void frameDidDraw() {
     if (!started) {
       started = true;
-      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) async {
+      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) async {
         _tester.start();
         registerDidStop(_tester.stop);
       });
@@ -141,22 +141,22 @@ class BenchMouseRegionMixedGridHover extends WidgetRecorder {
 class _UntilNextFrame {
   _UntilNextFrame._();
 
-  static Completer<void> _completer;
+  static Completer<void>? _completer;
 
   static Future<void> wait() {
     if (_UntilNextFrame._completer == null) {
       _UntilNextFrame._completer = Completer<void>();
-      SchedulerBinding.instance.addPostFrameCallback((_) {
-        _UntilNextFrame._completer.complete(null);
+      SchedulerBinding.instance!.addPostFrameCallback((_) {
+        _UntilNextFrame._completer!.complete(null);
         _UntilNextFrame._completer = null;
       });
     }
-    return _UntilNextFrame._completer.future;
+    return _UntilNextFrame._completer!.future;
   }
 }
 
 class _Tester {
-  _Tester({this.onDataPoint});
+  _Tester({required this.onDataPoint});
 
   final ValueSetter<Duration> onDataPoint;
 
@@ -167,12 +167,12 @@ class _Tester {
   TestGesture get gesture {
     return _gesture ??= TestGesture(
       dispatcher: (PointerEvent event) async {
-        RendererBinding.instance.handlePointerEvent(event);
+        RendererBinding.instance!.handlePointerEvent(event);
       },
       kind: PointerDeviceKind.mouse,
     );
   }
-  TestGesture _gesture;
+  TestGesture? _gesture;
 
   Duration currentTime = Duration.zero;
 

dev/benchmarks/macrobenchmarks/lib/src/web/bench_pageview_scroll_linethrough.dart

@@ -26,7 +26,7 @@ class BenchPageViewScrollLineThrough extends WidgetRecorder {
 }
 
 class _MyScrollContainer extends StatefulWidget {
-  const _MyScrollContainer({Key key}) : super(key: key);
+  const _MyScrollContainer({Key? key}) : super(key: key);
 
   @override
   State<_MyScrollContainer> createState() => _MyScrollContainerState();
@@ -35,7 +35,7 @@ class _MyScrollContainer extends StatefulWidget {
 class _MyScrollContainerState extends State<_MyScrollContainer> {
   static const Duration stepDuration = Duration(milliseconds: 500);
 
-  PageController pageController;
+  late PageController pageController;
   int pageNumber = 0;
 
   @override
@@ -56,8 +56,8 @@ class _MyScrollContainerState extends State<_MyScrollContainer> {
 
   @override
   void dispose() {
-    super.dispose();
     pageController.dispose();
+    super.dispose();
   }
 
   @override
@@ -77,8 +77,8 @@ class _CustomPainter extends CustomPainter {
   _CustomPainter(this.text);
 
   final String text;
-  Paint _linePainter;
-  TextPainter _textPainter;
+  final Paint _linePainter = Paint();
+  final TextPainter _textPainter = TextPainter();
   static const double lineWidth = 0.5;
 
   @override
@@ -91,14 +91,12 @@ class _CustomPainter extends CustomPainter {
     const double viewPadding = 5;
     const double circlePadding = 4;
     yPosition = viewPadding;
-    _textPainter = _textPainter ?? TextPainter();
     _textPainter.textDirection = TextDirection.ltr;
     _textPainter.textWidthBasis = TextWidthBasis.longestLine;
     _textPainter.textScaleFactor = 1;
     const TextStyle textStyle =
         TextStyle(color: Colors.black87, fontSize: 13, fontFamily: 'Roboto');
 
-    _linePainter = _linePainter ?? Paint();
     _linePainter.isAntiAlias = true;
     for (int i = 0; i < 42; i++) {
       _linePainter.color = Colors.white;

dev/benchmarks/macrobenchmarks/lib/src/web/bench_paths_recording.dart

@@ -7,218 +7,218 @@ import 'dart:ui';
 // The code below was generated by modify several parts of the engine
 // May 2020 and running Flutter Gallery.
 
-PathFillType gFillType;
-Rect gBounds;
-List<dynamic> allPaths;
-
-Path path8;
-Path path10;
-Path path12;
-Path path14;
-Path path16;
-Path path18;
-Path path34;
-Path path50;
-Path path60;
-Path path63;
-Path path66;
-Path path69;
-Path path72;
-Path path75;
-Path path78;
-Path path80;
-Path path82;
-Path path84;
-Path path86;
-Path path88;
-Path path119;
-Path path120;
-Path path121;
-Path path122;
-Path path123;
-Path path125;
-Path path127;
-Path path129;
-Path path131;
-Path path132;
-Path path134;
-Path path137;
-Path path140;
-Path path143;
-Path path145;
-Path path147;
-Path path208;
-Path path209;
-Path path210;
-Path path211;
-Path path213;
-Path path216;
-Path path219;
-Path path222;
-Path path225;
-Path path227;
-Path path229;
-Path path232;
-Path path235;
-Path path238;
-Path path240;
-Path path242;
-Path path277;
-Path path278;
-Path path279;
-Path path280;
-Path path281;
-Path path282;
-Path path284;
-Path path286;
-Path path288;
-Path path290;
-Path path292;
-Path path295;
-Path path298;
-Path path301;
-Path path330;
-Path path331;
-Path path332;
-Path path333;
-Path path334;
-Path path336;
-Path path338;
-Path path340;
-Path path342;
-Path path344;
-Path path345;
-Path path346;
-Path path349;
-Path path352;
-Path path356;
-Path path358;
-Path path359;
-Path path360;
-Path path361;
-Path path362;
-Path path363;
-Path path366;
-Path path369;
-Path path372;
-Path path373;
-Path path374;
-Path path375;
-Path path376;
-Path path379;
-Path path382;
-Path path385;
-Path path386;
-Path path387;
-Path path388;
-Path path389;
-Path path392;
-Path path395;
-Path path398;
-Path path399;
-Path path400;
-Path path401;
-Path path402;
-Path path405;
-Path path408;
-Path path411;
-Path path412;
-Path path413;
-Path path414;
-Path path415;
-Path path418;
-Path path421;
-Path path424;
-Path path425;
-Path path426;
-Path path427;
-Path path428;
-Path path431;
-Path path434;
-Path path437;
-Path path438;
-Path path439;
-Path path440;
-Path path441;
-Path path444;
-Path path447;
-Path path450;
-Path path451;
-Path path452;
-Path path453;
-Path path454;
-Path path457;
-Path path460;
-Path path463;
-Path path464;
-Path path465;
-Path path466;
-Path path467;
-Path path470;
-Path path473;
-Path path476;
-Path path477;
-Path path478;
-Path path479;
-Path path480;
-Path path483;
-Path path486;
-Path path489;
-Path path490;
-Path path491;
-Path path492;
-Path path493;
-Path path496;
-Path path499;
-Path path502;
-Path path503;
-Path path504;
-Path path505;
-Path path506;
-Path path509;
-Path path512;
-Path path515;
-Path path516;
-Path path517;
-Path path518;
-Path path519;
-Path path522;
-Path path525;
-Path path528;
-Path path529;
-Path path530;
-Path path531;
-Path path532;
-Path path535;
-Path path538;
-Path path541;
-Path path542;
-Path path543;
-Path path544;
-Path path545;
-Path path548;
-Path path551;
-Path path554;
-Path path555;
-Path path556;
-Path path557;
-Path path558;
-Path path561;
-Path path564;
-Path path573;
-Path path577;
-Path path579;
-Path path591;
-Path path592;
-Path path593;
-Path path594;
-Path path595;
-Path path597;
-Path path599;
-Path path601;
-Path path603;
-Path path606;
-Path path608;
+late PathFillType gFillType;
+late Rect gBounds;
+late List<dynamic> allPaths;
+
+late Path path8;
+late Path path10;
+late Path path12;
+late Path path14;
+late Path path16;
+late Path path18;
+late Path path34;
+late Path path50;
+late Path path60;
+late Path path63;
+late Path path66;
+late Path path69;
+late Path path72;
+late Path path75;
+late Path path78;
+late Path path80;
+late Path path82;
+late Path path84;
+late Path path86;
+late Path path88;
+late Path path119;
+late Path path120;
+late Path path121;
+late Path path122;
+late Path path123;
+late Path path125;
+late Path path127;
+late Path path129;
+late Path path131;
+late Path path132;
+late Path path134;
+late Path path137;
+late Path path140;
+late Path path143;
+late Path path145;
+late Path path147;
+late Path path208;
+late Path path209;
+late Path path210;
+late Path path211;
+late Path path213;
+late Path path216;
+late Path path219;
+late Path path222;
+late Path path225;
+late Path path227;
+late Path path229;
+late Path path232;
+late Path path235;
+late Path path238;
+late Path path240;
+late Path path242;
+late Path path277;
+late Path path278;
+late Path path279;
+late Path path280;
+late Path path281;
+late Path path282;
+late Path path284;
+late Path path286;
+late Path path288;
+late Path path290;
+late Path path292;
+late Path path295;
+late Path path298;
+late Path path301;
+late Path path330;
+late Path path331;
+late Path path332;
+late Path path333;
+late Path path334;
+late Path path336;
+late Path path338;
+late Path path340;
+late Path path342;
+late Path path344;
+late Path path345;
+late Path path346;
+late Path path349;
+late Path path352;
+late Path path356;
+late Path path358;
+late Path path359;
+late Path path360;
+late Path path361;
+late Path path362;
+late Path path363;
+late Path path366;
+late Path path369;
+late Path path372;
+late Path path373;
+late Path path374;
+late Path path375;
+late Path path376;
+late Path path379;
+late Path path382;
+late Path path385;
+late Path path386;
+late Path path387;
+late Path path388;
+late Path path389;
+late Path path392;
+late Path path395;
+late Path path398;
+late Path path399;
+late Path path400;
+late Path path401;
+late Path path402;
+late Path path405;
+late Path path408;
+late Path path411;
+late Path path412;
+late Path path413;
+late Path path414;
+late Path path415;
+late Path path418;
+late Path path421;
+late Path path424;
+late Path path425;
+late Path path426;
+late Path path427;
+late Path path428;
+late Path path431;
+late Path path434;
+late Path path437;
+late Path path438;
+late Path path439;
+late Path path440;
+late Path path441;
+late Path path444;
+late Path path447;
+late Path path450;
+late Path path451;
+late Path path452;
+late Path path453;
+late Path path454;
+late Path path457;
+late Path path460;
+late Path path463;
+late Path path464;
+late Path path465;
+late Path path466;
+late Path path467;
+late Path path470;
+late Path path473;
+late Path path476;
+late Path path477;
+late Path path478;
+late Path path479;
+late Path path480;
+late Path path483;
+late Path path486;
+late Path path489;
+late Path path490;
+late Path path491;
+late Path path492;
+late Path path493;
+late Path path496;
+late Path path499;
+late Path path502;
+late Path path503;
+late Path path504;
+late Path path505;
+late Path path506;
+late Path path509;
+late Path path512;
+late Path path515;
+late Path path516;
+late Path path517;
+late Path path518;
+late Path path519;
+late Path path522;
+late Path path525;
+late Path path528;
+late Path path529;
+late Path path530;
+late Path path531;
+late Path path532;
+late Path path535;
+late Path path538;
+late Path path541;
+late Path path542;
+late Path path543;
+late Path path544;
+late Path path545;
+late Path path548;
+late Path path551;
+late Path path554;
+late Path path555;
+late Path path556;
+late Path path557;
+late Path path558;
+late Path path561;
+late Path path564;
+late Path path573;
+late Path path577;
+late Path path579;
+late Path path591;
+late Path path592;
+late Path path593;
+late Path path594;
+late Path path595;
+late Path path597;
+late Path path599;
+late Path path601;
+late Path path603;
+late Path path606;
+late Path path608;
 
 void createPaths() {
   allPaths = <dynamic>[];

dev/benchmarks/macrobenchmarks/lib/src/web/bench_picture_recording.dart

@@ -26,12 +26,12 @@ class BenchPictureRecording extends RawRecorder {
   /// Cached paint used for drawing.
   ///
   /// We want to avoid polluting the results with paint initialization logic.
-  Paint paint;
+  late Paint paint;
 
   /// A prelaid out and cached paragraph.
   ///
   /// This is cached to remove text layout time from the benchmark time.
-  Paragraph paragraph;
+  late Paragraph paragraph;
 
   @override
   Future<void> setUpAll() async {

dev/benchmarks/macrobenchmarks/lib/src/web/bench_simple_lazy_text_scroll.dart

@@ -56,9 +56,9 @@ class BenchSimpleLazyTextScroll extends WidgetRecorder {
 
 class _TestScrollingWidget extends StatefulWidget {
   const _TestScrollingWidget({
-    @required this.initialScrollOffset,
-    @required this.scrollDistance,
-    @required this.scrollDuration,
+    required this.initialScrollOffset,
+    required this.scrollDistance,
+    required this.scrollDuration,
   });
 
   final double initialScrollOffset;
@@ -72,7 +72,7 @@ class _TestScrollingWidget extends StatefulWidget {
 }
 
 class _TestScrollingWidgetState extends State<_TestScrollingWidget> {
-  ScrollController scrollController;
+  late ScrollController scrollController;
 
   @override
   void initState() {
@@ -98,6 +98,12 @@ class _TestScrollingWidgetState extends State<_TestScrollingWidget> {
     });
   }
 
+  @override
+  void dispose() {
+    scrollController.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     return ListView.builder(

dev/benchmarks/macrobenchmarks/lib/src/web/bench_text_layout.dart

@@ -31,7 +31,7 @@ class ParagraphGenerator {
   /// font-size so that the engine doesn't reuse a cached ruler.
   ui.Paragraph generate(
     String text, {
-    int maxLines,
+    int? maxLines,
     bool hasEllipsis = false,
   }) {
     final ui.ParagraphBuilder builder = ui.ParagraphBuilder(ui.ParagraphStyle(
@@ -61,8 +61,8 @@ enum _TestMode {
 
 /// Sends a platform message to the web engine to enable/disable the usage of
 /// the canvas-based text measurement implementation.
-void _setTestMode(_TestMode mode) {
-  bool useCanvasText; // null means do not force DOM or canvas, works for CanvasKit
+void _setTestMode(_TestMode? mode) {
+  bool? useCanvasText; // null means do not force DOM or canvas, works for CanvasKit
   switch (mode) {
     case _TestMode.useDomTextLayout:
       useCanvasText = false;
@@ -148,11 +148,11 @@ class BenchTextLayout extends RawRecorder {
   }
 
   void recordParagraphOperations({
-    @required Profile profile,
-    @required ui.Paragraph paragraph,
-    @required String text,
-    @required String keyPrefix,
-    @required double maxWidth,
+    required Profile profile,
+    required ui.Paragraph paragraph,
+    required String text,
+    required String keyPrefix,
+    required double maxWidth,
   }) {
     profile.record('$keyPrefix.layout', () {
       paragraph.layout(ui.ParagraphConstraints(width: maxWidth));
@@ -277,7 +277,7 @@ class BenchBuildColorsGrid extends WidgetBuildRecorder {
     // updates the value of [showWidget] in preparation for the next frame.
     // TODO(yjbanov): https://github.com/flutter/flutter/issues/53877
     if (showWidget && _mode != _TestMode.useCanvasKit) {
-      profile.addDataPoint(
+      profile!.addDataPoint(
         'text_layout',
         Duration(microseconds: _textLayoutMicros.toInt()),
         reported: true,
@@ -299,15 +299,13 @@ class BenchBuildColorsGrid extends WidgetBuildRecorder {
 const double kColorItemHeight = 48.0;
 
 class Palette {
-  Palette({this.name, this.primary, this.accent, this.threshold = 900});
+  Palette({required this.name, required this.primary, this.accent, this.threshold = 900});
 
   final String name;
   final MaterialColor primary;
-  final MaterialAccentColor accent;
+  final MaterialAccentColor? accent;
   final int
       threshold; // titles for indices > threshold are white, otherwise black
-
-  bool get isValid => name != null && primary != null && threshold != null;
 }
 
 final List<Palette> allPalettes = <Palette>[
@@ -390,9 +388,9 @@ final List<Palette> allPalettes = <Palette>[
 
 class ColorItem extends StatelessWidget {
   const ColorItem({
-    Key key,
-    @required this.index,
-    @required this.color,
+    Key? key,
+    required this.index,
+    required this.color,
     this.prefix = '',
   })  : assert(index != null),
         assert(color != null),
@@ -432,11 +430,10 @@ class ColorItem extends StatelessWidget {
 }
 
 class PaletteTabView extends StatelessWidget {
-  PaletteTabView({
-    Key key,
-    @required this.colors,
-  })  : assert(colors != null && colors.isValid),
-        super(key: key);
+  const PaletteTabView({
+    Key? key,
+    required this.colors,
+  }) : super(key: key);
 
   final Palette colors;
 
@@ -458,9 +455,9 @@ class PaletteTabView extends StatelessWidget {
   Widget build(BuildContext context) {
     final TextTheme textTheme = Theme.of(context).textTheme;
     final TextStyle whiteTextStyle =
-        textTheme.bodyText2.copyWith(color: Colors.white);
+        textTheme.bodyText2!.copyWith(color: Colors.white);
     final TextStyle blackTextStyle =
-        textTheme.bodyText2.copyWith(color: Colors.black);
+        textTheme.bodyText2!.copyWith(color: Colors.black);
     return Scrollbar(
       child: ListView(
         itemExtent: kColorItemHeight,
@@ -468,7 +465,7 @@ class PaletteTabView extends StatelessWidget {
           ...primaryKeys.map<Widget>((int index) {
             return DefaultTextStyle(
               style: index > colors.threshold ? whiteTextStyle : blackTextStyle,
-              child: ColorItem(index: index, color: colors.primary[index]),
+              child: ColorItem(index: index, color: colors.primary[index]!),
             );
           }),
           if (colors.accent != null)
@@ -477,7 +474,7 @@ class PaletteTabView extends StatelessWidget {
                 style:
                     index > colors.threshold ? whiteTextStyle : blackTextStyle,
                 child: ColorItem(
-                    index: index, color: colors.accent[index], prefix: 'A'),
+                    index: index, color: colors.accent![index]!, prefix: 'A'),
               );
             }),
         ],
@@ -487,7 +484,7 @@ class PaletteTabView extends StatelessWidget {
 }
 
 class ColorsDemo extends StatelessWidget {
-  const ColorsDemo({Key key}) : super(key: key);
+  const ColorsDemo({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

dev/benchmarks/macrobenchmarks/lib/src/web/bench_text_out_of_picture_bounds.dart

@@ -54,8 +54,8 @@ class BenchTextOutOfPictureBounds extends SceneBuilderRecorder {
 
   static const String benchmarkName = 'text_out_of_picture_bounds';
 
-  List<Paragraph> singleLineParagraphs;
-  List<Paragraph> multiLineParagraphs;
+  late List<Paragraph> singleLineParagraphs;
+  late List<Paragraph> multiLineParagraphs;
 
   @override
   void onDrawFrame(SceneBuilder sceneBuilder) {

dev/benchmarks/macrobenchmarks/lib/src/web/bench_wrapbox_scroll.dart

@@ -29,16 +29,14 @@ class BenchWrapBoxScroll extends WidgetRecorder {
 }
 
 class MyHomePage extends StatefulWidget {
-  const MyHomePage({Key key, this.title}) : super(key: key);
-
-  final String title;
+  const MyHomePage({Key? key}) : super(key: key);
 
   @override
   State<MyHomePage> createState() => _MyHomePageState();
 }
 
 class _MyHomePageState extends State<MyHomePage> {
-  ScrollController scrollController;
+  late ScrollController scrollController;
   int block = 0;
   static const Duration stepDuration = Duration(milliseconds: 500);
   static const double stepDistance = 400;
@@ -61,8 +59,8 @@ class _MyHomePageState extends State<MyHomePage> {
 
   @override
   void dispose() {
-    super.dispose();
     scrollController.dispose();
+    super.dispose();
   }
 
   @override
@@ -84,7 +82,7 @@ class _MyHomePageState extends State<MyHomePage> {
 }
 
 class ProductPreview extends StatelessWidget {
-  const ProductPreview(this.previewIndex, {Key key}) : super(key: key);
+  const ProductPreview(this.previewIndex, {Key? key}) : super(key: key);
 
   final int previewIndex;
 
@@ -143,8 +141,8 @@ class ProductPreview extends StatelessWidget {
 
 class ProductOption extends StatelessWidget {
   const ProductOption({
-    Key key,
-    @required this.optionText,
+    Key? key,
+    required this.optionText,
   }) : super(key: key);
 
   final String optionText;

dev/benchmarks/macrobenchmarks/lib/src/web/recorder.dart

@@ -63,7 +63,7 @@ class Runner {
   ///
   /// All arguments must not be null.
   Runner({
-    @required this.recorder,
+    required this.recorder,
     this.setUpAllDidRun = _dummyAsyncVoidCallback,
     this.tearDownAllWillRun = _dummyAsyncVoidCallback,
   });
@@ -113,13 +113,13 @@ abstract class Recorder {
   /// Returns the recorded profile.
   ///
   /// This value is only available while the benchmark is running.
-  Profile get profile;
+  Profile? get profile;
 
   /// Whether the benchmark should continue running.
   ///
   /// Returns `false` if the benchmark collected enough data and it's time to
   /// stop.
-  bool shouldContinue() => profile.shouldContinue();
+  bool shouldContinue() => profile?.shouldContinue() ?? true;
 
   /// Called once before all runs of this benchmark recorder.
   ///
@@ -161,7 +161,7 @@ abstract class Recorder {
 /// }
 /// ```
 abstract class RawRecorder extends Recorder {
-  RawRecorder({@required String name}) : super._(name, false);
+  RawRecorder({required String name}) : super._(name, false);
 
   /// The body of the benchmark.
   ///
@@ -169,8 +169,8 @@ abstract class RawRecorder extends Recorder {
   void body(Profile profile);
 
   @override
-  Profile get profile => _profile;
-  Profile _profile;
+  Profile? get profile => _profile;
+  Profile? _profile;
 
   @override
   @nonVirtual
@@ -178,9 +178,9 @@ abstract class RawRecorder extends Recorder {
     _profile = Profile(name: name);
     do {
       await Future<void>.delayed(Duration.zero);
-      body(_profile);
+      body(_profile!);
     } while (shouldContinue());
-    return _profile;
+    return _profile!;
   }
 }
 
@@ -210,11 +210,11 @@ abstract class RawRecorder extends Recorder {
 /// }
 /// ```
 abstract class SceneBuilderRecorder extends Recorder {
-  SceneBuilderRecorder({@required String name}) : super._(name, true);
+  SceneBuilderRecorder({required String name}) : super._(name, true);
 
   @override
-  Profile get profile => _profile;
-  Profile _profile;
+  Profile? get profile => _profile;
+  Profile? _profile;
 
   /// Called from [dart:ui.PlatformDispatcher.onBeginFrame].
   @mustCallSuper
@@ -235,7 +235,7 @@ abstract class SceneBuilderRecorder extends Recorder {
 
     window.onBeginFrame = (_) {
       try {
-        startMeasureFrame(profile);
+        startMeasureFrame(profile!);
         onBeginFrame();
       } catch (error, stackTrace) {
         profileCompleter.completeError(error, stackTrace);
@@ -244,12 +244,12 @@ abstract class SceneBuilderRecorder extends Recorder {
     };
     window.onDrawFrame = () {
       try {
-        _profile.record('drawFrameDuration', () {
+        _profile!.record('drawFrameDuration', () {
           final SceneBuilder sceneBuilder = SceneBuilder();
           onDrawFrame(sceneBuilder);
-          _profile.record('sceneBuildDuration', () {
+          _profile!.record('sceneBuildDuration', () {
             final Scene scene = sceneBuilder.build();
-            _profile.record('windowRenderDuration', () {
+            _profile!.record('windowRenderDuration', () {
               window.render(scene);
             }, reported: false);
           }, reported: false);
@@ -334,7 +334,7 @@ abstract class SceneBuilderRecorder extends Recorder {
 /// ```
 abstract class WidgetRecorder extends Recorder implements FrameRecorder {
   WidgetRecorder({
-    @required String name,
+    required String name,
     this.useCustomWarmUp = false,
   }) : super._(name, true);
 
@@ -352,18 +352,18 @@ abstract class WidgetRecorder extends Recorder implements FrameRecorder {
   }
 
   @override
-  Profile profile;
-  Completer<void> _runCompleter;
+  Profile? profile;
+  Completer<void>? _runCompleter;
 
   /// Whether to delimit warm-up frames in a custom way.
   final bool useCustomWarmUp;
 
-  Stopwatch _drawFrameStopwatch;
+  late Stopwatch _drawFrameStopwatch;
 
   @override
   @mustCallSuper
   void frameWillDraw() {
-    startMeasureFrame(profile);
+    startMeasureFrame(profile!);
     _drawFrameStopwatch = Stopwatch()..start();
   }
 
@@ -371,20 +371,20 @@ abstract class WidgetRecorder extends Recorder implements FrameRecorder {
   @mustCallSuper
   void frameDidDraw() {
     endMeasureFrame();
-    profile.addDataPoint('drawFrameDuration', _drawFrameStopwatch.elapsed, reported: true);
+    profile!.addDataPoint('drawFrameDuration', _drawFrameStopwatch.elapsed, reported: true);
 
     if (shouldContinue()) {
       window.scheduleFrame();
     } else {
       for (final VoidCallback fn in _didStopCallbacks)
         fn();
-      _runCompleter.complete();
+      _runCompleter!.complete();
     }
   }
 
   @override
-  void _onError(dynamic error, StackTrace stackTrace) {
-    _runCompleter.completeError(error, stackTrace);
+  void _onError(Object error, StackTrace? stackTrace) {
+    _runCompleter!.completeError(error, stackTrace);
   }
 
   @override
@@ -413,7 +413,7 @@ abstract class WidgetRecorder extends Recorder implements FrameRecorder {
     binding._beginRecording(this, widget);
 
     try {
-      await _runCompleter.future;
+      await _runCompleter!.future;
       return localProfile;
     } finally {
       stopListeningToEngineBenchmarkValues(kProfilePrerollFrame);
@@ -432,7 +432,7 @@ abstract class WidgetRecorder extends Recorder implements FrameRecorder {
 /// performance of frames that render the widget and ignoring the frames that
 /// clear the screen.
 abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
-  WidgetBuildRecorder({@required String name}) : super._(name, true);
+  WidgetBuildRecorder({required String name}) : super._(name, true);
 
   /// Creates a widget to be benchmarked.
   ///
@@ -448,10 +448,10 @@ abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
   }
 
   @override
-  Profile profile;
-  Completer<void> _runCompleter;
+  Profile? profile;
+  Completer<void>? _runCompleter;
 
-  Stopwatch _drawFrameStopwatch;
+  late Stopwatch _drawFrameStopwatch;
 
   /// Whether in this frame we should call [createWidget] and render it.
   ///
@@ -459,9 +459,9 @@ abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
   bool showWidget = true;
 
   /// The state that hosts the widget under test.
-  _WidgetBuildRecorderHostState _hostState;
+  late _WidgetBuildRecorderHostState _hostState;
 
-  Widget _getWidgetForFrame() {
+  Widget? _getWidgetForFrame() {
     if (showWidget) {
       return createWidget();
     } else {
@@ -473,7 +473,7 @@ abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
   @mustCallSuper
   void frameWillDraw() {
     if (showWidget) {
-      startMeasureFrame(profile);
+      startMeasureFrame(profile!);
       _drawFrameStopwatch = Stopwatch()..start();
     }
   }
@@ -484,7 +484,7 @@ abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
     // Only record frames that show the widget.
     if (showWidget) {
       endMeasureFrame();
-      profile.addDataPoint('drawFrameDuration', _drawFrameStopwatch.elapsed, reported: true);
+      profile!.addDataPoint('drawFrameDuration', _drawFrameStopwatch.elapsed, reported: true);
     }
 
     if (shouldContinue()) {
@@ -493,13 +493,13 @@ abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
     } else {
       for (final VoidCallback fn in _didStopCallbacks)
         fn();
-      _runCompleter.complete();
+      _runCompleter!.complete();
     }
   }
 
   @override
-  void _onError(dynamic error, StackTrace stackTrace) {
-    _runCompleter.completeError(error, stackTrace);
+  void _onError(Object error, StackTrace? stackTrace) {
+    _runCompleter!.completeError(error, stackTrace);
   }
 
   @override
@@ -511,7 +511,7 @@ abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
     binding._beginRecording(this, _WidgetBuildRecorderHost(this));
 
     try {
-      await _runCompleter.future;
+      await _runCompleter!.future;
       return localProfile;
     } finally {
       _runCompleter = null;
@@ -578,11 +578,11 @@ class Timeseries {
 
   /// The number of frames ignored as warm-up frames, used only
   /// when [useCustomWarmUp] is true.
-  int _warmUpFrameCount;
+  int? _warmUpFrameCount;
 
   /// The number of frames ignored as warm-up frames.
   int get warmUpFrameCount => useCustomWarmUp
-      ? _warmUpFrameCount
+      ? _warmUpFrameCount!
       : count - _kMeasuredSampleCount;
 
   /// List of all the values that have been recorded.
@@ -664,7 +664,7 @@ class Timeseries {
   }
 
   /// Adds a value to this timeseries.
-  void add(double value, {@required bool isWarmUpValue}) {
+  void add(double value, {required bool isWarmUpValue}) {
     if (value < 0.0) {
       throw StateError(
         'Timeseries $name: negative metric values are not supported. Got: $value',
@@ -672,7 +672,7 @@ class Timeseries {
     }
     _allValues.add(value);
     if (useCustomWarmUp && isWarmUpValue) {
-      _warmUpFrameCount += 1;
+      _warmUpFrameCount = (_warmUpFrameCount ?? 0) + 1;
     }
   }
 }
@@ -683,15 +683,15 @@ class Timeseries {
 @sealed
 class TimeseriesStats {
   const TimeseriesStats({
-    @required this.name,
-    @required this.average,
-    @required this.outlierCutOff,
-    @required this.outlierAverage,
-    @required this.standardDeviation,
-    @required this.noise,
-    @required this.cleanSampleCount,
-    @required this.outlierSampleCount,
-    @required this.samples,
+    required this.name,
+    required this.average,
+    required this.outlierCutOff,
+    required this.outlierAverage,
+    required this.standardDeviation,
+    required this.noise,
+    required this.cleanSampleCount,
+    required this.outlierSampleCount,
+    required this.samples,
   });
 
   /// The label used to refer to the corresponding timeseries.
@@ -764,9 +764,9 @@ class TimeseriesStats {
 @sealed
 class AnnotatedSample {
   const AnnotatedSample({
-    @required this.magnitude,
-    @required this.isOutlier,
-    @required this.isWarmUpValue,
+    required this.magnitude,
+    required this.isOutlier,
+    required this.isWarmUpValue,
   });
 
   /// The non-negative raw result of the measurement.
@@ -787,7 +787,7 @@ class AnnotatedSample {
 
 /// Base class for a profile collected from running a benchmark.
 class Profile {
-  Profile({@required this.name, this.useCustomWarmUp = false})
+  Profile({required this.name, this.useCustomWarmUp = false})
       : assert(name != null),
         _isWarmingUp = useCustomWarmUp;
 
@@ -824,7 +824,7 @@ class Profile {
   final Map<String, dynamic> extraData = <String, dynamic>{};
 
   /// Invokes [callback] and records the duration of its execution under [key].
-  Duration record(String key, VoidCallback callback, { @required bool reported }) {
+  Duration record(String key, VoidCallback callback, { required bool reported }) {
     final Duration duration = timeAction(callback);
     addDataPoint(key, duration, reported: reported);
     return duration;
@@ -836,7 +836,7 @@ class Profile {
   ///
   /// Set [reported] to `false` to store the data, but not show it on the
   /// dashboard UI.
-  void addDataPoint(String key, Duration duration, { @required bool reported }) {
+  void addDataPoint(String key, Duration duration, { required bool reported }) {
     scoreData.putIfAbsent(
         key,
         () => Timeseries(key, reported, useCustomWarmUp: useCustomWarmUp),
@@ -860,7 +860,7 @@ class Profile {
 
     // We have recorded something, but do we have enough samples? If every
     // timeseries has collected enough samples, stop the benchmark.
-    return !scoreData.keys.every((String key) => scoreData[key].count >= kTotalSampleCount);
+    return !scoreData.keys.every((String key) => scoreData[key]!.count >= kTotalSampleCount);
   }
 
   /// Returns a JSON representation of the profile that will be sent to the
@@ -873,7 +873,7 @@ class Profile {
     };
 
     for (final String key in scoreData.keys) {
-      final Timeseries timeseries = scoreData[key];
+      final Timeseries timeseries = scoreData[key]!;
 
       if (timeseries.isReported) {
         scoreKeys.add('$key.average');
@@ -900,7 +900,7 @@ class Profile {
     final StringBuffer buffer = StringBuffer();
     buffer.writeln('name: $name');
     for (final String key in scoreData.keys) {
-      final Timeseries timeseries = scoreData[key];
+      final Timeseries timeseries = scoreData[key]!;
       final TimeseriesStats stats = timeseries.computeStats();
       buffer.writeln(stats.toString());
     }
@@ -967,7 +967,7 @@ abstract class FrameRecorder {
   /// Reports an error.
   ///
   /// The implementation is expected to halt benchmark execution as soon as possible.
-  void _onError(dynamic error, StackTrace stackTrace);
+  void _onError(Object error, StackTrace? stackTrace);
 }
 
 /// A variant of [WidgetsBinding] that collaborates with a [Recorder] to decide
@@ -992,10 +992,10 @@ class _RecordingWidgetsBinding extends BindingBase
     if (WidgetsBinding.instance == null) {
       _RecordingWidgetsBinding();
     }
-    return WidgetsBinding.instance as _RecordingWidgetsBinding;
+    return WidgetsBinding.instance! as _RecordingWidgetsBinding;
   }
 
-  FrameRecorder _recorder;
+  FrameRecorder? _recorder;
   bool _hasErrored = false;
 
   /// To short-circuit all frame lifecycle methods when the benchmark has
@@ -1008,7 +1008,7 @@ class _RecordingWidgetsBinding extends BindingBase
         'Cannot call _RecordingWidgetsBinding._beginRecording more than once',
       );
     }
-    final FlutterExceptionHandler originalOnError = FlutterError.onError;
+    final FlutterExceptionHandler? originalOnError = FlutterError.onError;
 
     recorder.registerDidStop(() {
       _benchmarkStopped = true;
@@ -1017,22 +1017,22 @@ class _RecordingWidgetsBinding extends BindingBase
     // Fail hard and fast on errors. Benchmarks should not have any errors.
     FlutterError.onError = (FlutterErrorDetails details) {
       _haltBenchmarkWithError(details.exception, details.stack);
-      originalOnError(details);
+      originalOnError?.call(details);
     };
     _recorder = recorder;
     runApp(widget);
   }
 
-  void _haltBenchmarkWithError(dynamic error, StackTrace stackTrace) {
+  void _haltBenchmarkWithError(Object error, StackTrace? stackTrace) {
     if (_hasErrored) {
       return;
     }
-    _recorder._onError(error, stackTrace);
+    _recorder?._onError(error, stackTrace);
     _hasErrored = true;
   }
 
   @override
-  void handleBeginFrame(Duration rawTimeStamp) {
+  void handleBeginFrame(Duration? rawTimeStamp) {
     // Don't keep on truckin' if there's an error or the benchmark has stopped.
     if (_hasErrored || _benchmarkStopped) {
       return;
@@ -1061,9 +1061,9 @@ class _RecordingWidgetsBinding extends BindingBase
       return;
     }
     try {
-      _recorder.frameWillDraw();
+      _recorder?.frameWillDraw();
       super.handleDrawFrame();
-      _recorder.frameDidDraw();
+      _recorder?.frameDidDraw();
     } catch (error, stackTrace) {
       _haltBenchmarkWithError(error, stackTrace);
       rethrow;
@@ -1189,7 +1189,7 @@ void stopListeningToEngineBenchmarkValues(String name) {
 //
 // If there are no listeners registered for [name], ignores the value.
 void _dispatchEngineBenchmarkValue(String name, double value) {
-  final EngineBenchmarkValueListener listener = _engineBenchmarkListeners[name];
+  final EngineBenchmarkValueListener? listener = _engineBenchmarkListeners[name];
   if (listener != null) {
     listener(value);
   }

dev/benchmarks/macrobenchmarks/lib/src/web/test_data.dart

@@ -5,8 +5,6 @@
 import 'dart:math' as math;
 import 'dart:ui';
 
-import 'package:meta/meta.dart';
-
 // Used to randomize data.
 //
 // Using constant seed for reproducibility.
@@ -34,11 +32,11 @@ final List<String> lipsum = 'Lorem ipsum dolor sit amet, consectetur adipiscing
 /// Generates strings and builds pre-laid out paragraphs to be used by
 /// benchmarks.
 List<Paragraph> generateLaidOutParagraphs({
-  @required int paragraphCount,
-  @required int minWordCountPerParagraph,
-  @required int maxWordCountPerParagraph,
-  @required double widthConstraint,
-  @required Color color,
+  required int paragraphCount,
+  required int minWordCountPerParagraph,
+  required int maxWordCountPerParagraph,
+  required double widthConstraint,
+  required Color color,
 }) {
   final List<Paragraph> strings = <Paragraph>[];
   int wordPointer = 0; // points to the next word in lipsum to extract

dev/benchmarks/macrobenchmarks/lib/web_benchmarks.dart

@@ -93,7 +93,7 @@ Future<void> main() async {
 }
 
 Future<void> _runBenchmark(String benchmarkName) async {
-  final RecorderFactory recorderFactory = benchmarks[benchmarkName];
+  final RecorderFactory? recorderFactory = benchmarks[benchmarkName];
 
   if (recorderFactory == null) {
     _fallbackToManual('Benchmark $benchmarkName not found.');
@@ -145,7 +145,7 @@ Future<void> _runBenchmark(String benchmarkName) async {
 }
 
 void _fallbackToManual(String error) {
-  html.document.body.appendHtml('''
+  html.document.body!.appendHtml('''
     <div id="manual-panel">
       <h3>$error</h3>
 
@@ -163,9 +163,9 @@ void _fallbackToManual(String error) {
   ''', validator: html.NodeValidatorBuilder()..allowHtml5()..allowInlineStyles());
 
   for (final String benchmarkName in benchmarks.keys) {
-    final html.Element button = html.document.querySelector('#$benchmarkName');
+    final html.Element button = html.document.querySelector('#$benchmarkName')!;
     button.addEventListener('click', (_) {
-      final html.Element manualPanel = html.document.querySelector('#manual-panel');
+      final html.Element? manualPanel = html.document.querySelector('#manual-panel');
       manualPanel?.remove();
       _runBenchmark(benchmarkName);
     });
@@ -174,14 +174,14 @@ void _fallbackToManual(String error) {
 
 /// Visualizes results on the Web page for manual inspection.
 void _printResultsToScreen(Profile profile) {
-  html.document.body.remove();
+  html.document.body!.remove();
   html.document.body = html.BodyElement();
-  html.document.body.appendHtml('<h2>${profile.name}</h2>');
+  html.document.body!.appendHtml('<h2>${profile.name}</h2>');
 
   profile.scoreData.forEach((String scoreKey, Timeseries timeseries) {
-    html.document.body.appendHtml('<h2>$scoreKey</h2>');
-    html.document.body.appendHtml('<pre>${timeseries.computeStats()}</pre>');
-    html.document.body.append(TimeseriesVisualization(timeseries).render());
+    html.document.body!.appendHtml('<h2>$scoreKey</h2>');
+    html.document.body!.appendHtml('<pre>${timeseries.computeStats()}</pre>');
+    html.document.body!.append(TimeseriesVisualization(timeseries).render());
   });
 }
 
@@ -190,7 +190,7 @@ class TimeseriesVisualization {
   TimeseriesVisualization(this._timeseries) {
     _stats = _timeseries.computeStats();
     _canvas = html.CanvasElement();
-    _screenWidth = html.window.screen.width;
+    _screenWidth = html.window.screen!.width!;
     _canvas.width = _screenWidth;
     _canvas.height = (_kCanvasHeight * html.window.devicePixelRatio).round();
     _canvas.style
@@ -211,13 +211,13 @@ class TimeseriesVisualization {
   static const double _kCanvasHeight = 200;
 
   final Timeseries _timeseries;
-  TimeseriesStats _stats;
-  html.CanvasElement _canvas;
-  html.CanvasRenderingContext2D _ctx;
-  int _screenWidth;
+  late TimeseriesStats _stats;
+  late html.CanvasElement _canvas;
+  late html.CanvasRenderingContext2D _ctx;
+  late int _screenWidth;
 
   // Used to normalize benchmark values to chart height.
-  double _maxValueChartRange;
+  late double _maxValueChartRange;
 
   /// Converts a sample value to vertical canvas coordinates.
   ///
@@ -300,7 +300,7 @@ class LocalBenchmarkServerClient {
   /// This happens when you run benchmarks using plain `flutter run` rather than
   /// devicelab test harness. The test harness spins up a special server that
   /// provides API for automatically picking the next benchmark to run.
-  bool isInManualMode;
+  bool isInManualMode = false;
 
   /// Asks the local server for the name of the next benchmark to run.
   ///
@@ -323,7 +323,7 @@ class LocalBenchmarkServerClient {
     }
 
     isInManualMode = false;
-    return request.responseText;
+    return request.responseText!;
   }
 
   void _checkNotManualMode() {
@@ -405,11 +405,11 @@ class LocalBenchmarkServerClient {
   /// crash on 404, which we use to detect `flutter run`.
   Future<html.HttpRequest> _requestXhr(
     String url, {
-    String method,
-    bool withCredentials,
-    String responseType,
-    String mimeType,
-    Map<String, String> requestHeaders,
+    String? method,
+    bool? withCredentials,
+    String? responseType,
+    String? mimeType,
+    Map<String, String>? requestHeaders,
     dynamic sendData,
   }) {
     final Completer<html.HttpRequest> completer = Completer<html.HttpRequest>();

dev/benchmarks/macrobenchmarks/pubspec.yaml

@@ -2,7 +2,7 @@ name: macrobenchmarks
 description: Performance benchmarks using flutter drive.
 
 environment:
-  sdk: ">=2.2.2 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:

dev/benchmarks/macrobenchmarks/test/frame_policy.dart

@@ -74,7 +74,7 @@ void main() {
       frameCount = 0;
       delays = await tester.handlePointerEventRecord(records);
       await tester.pumpAndSettle();
-      binding.reportData['fullyLive'] = _summarizeResult(frameCount, delays);
+      binding.reportData!['fullyLive'] = _summarizeResult(frameCount, delays);
       await tester.idle();
     },
   );

dev/benchmarks/macrobenchmarks/test/util.dart

@@ -13,10 +13,10 @@ typedef ControlCallback = Future<void> Function(WidgetController controller);
 void macroPerfTestE2E(
   String testName,
   String routeName, {
-  Duration pageDelay,
+  Duration? pageDelay,
   Duration duration = const Duration(seconds: 3),
-  ControlCallback body,
-  ControlCallback setup,
+  ControlCallback? body,
+  ControlCallback? setup,
 }) {
   final WidgetsBinding _binding = IntegrationTestWidgetsFlutterBinding.ensureInitialized();
   assert(_binding is IntegrationTestWidgetsFlutterBinding);

dev/benchmarks/macrobenchmarks/test_driver/animated_image.dart

@@ -15,7 +15,7 @@ import 'package:macrobenchmarks/src/animated_image.dart';
 /// set number of image frames to render.
 Future<void> main() async {
   final Completer<void> waiter = Completer<void>();
-  enableFlutterDriverExtension(handler: (String request) async {
+  enableFlutterDriverExtension(handler: (String? request) async {
     if (request != 'waitForAnimation') {
       throw UnsupportedError('Unrecognized request $request');
     }

dev/benchmarks/macrobenchmarks/test_driver/e2e_test.dart

@@ -5,9 +5,9 @@
 import 'package:integration_test/integration_test_driver.dart' as driver;
 
 Future<void> main() => driver.integrationDriver(
-  responseDataCallback: (Map<String, dynamic> data) async {
+  responseDataCallback: (Map<String, dynamic>? data) async {
     await driver.writeResponseData(
-      data['performance'] as Map<String, dynamic>,
+      data?['performance'] as Map<String, dynamic>,
       testOutputFilename: 'e2e_perf_summary',
     );
   }

dev/benchmarks/macrobenchmarks/test_driver/frame_policy_test.dart

@@ -7,11 +7,11 @@ import 'dart:io';
 import 'package:integration_test/integration_test_driver.dart' as driver;
 
 Future<void> main() => driver.integrationDriver(
-  responseDataCallback: (Map<String, dynamic> data) async {
+  responseDataCallback: (Map<String, dynamic>? data) async {
     final Map<String, dynamic> benchmarkLiveResult =
-        data['benchmarkLive'] as Map<String,dynamic>;
+        data?['benchmarkLive'] as Map<String,dynamic>;
     final Map<String, dynamic> fullyLiveResult =
-        data['fullyLive'] as Map<String,dynamic>;
+        data?['fullyLive'] as Map<String,dynamic>;
 
     if(benchmarkLiveResult['frame_count'] as int < 10
        || fullyLiveResult['frame_count'] as int < 10) {

dev/benchmarks/macrobenchmarks/test_driver/large_image_changer.dart

@@ -11,7 +11,7 @@ import 'package:macrobenchmarks/common.dart';
 import 'package:macrobenchmarks/main.dart';
 
 Future<void> main() async {
-  enableFlutterDriverExtension(handler: (String message) async {
+  enableFlutterDriverExtension(handler: (String? message) async {
     if (message == 'getTargetPlatform') {
       return defaultTargetPlatform.toString();
     }

dev/benchmarks/macrobenchmarks/test_driver/large_image_changer_test.dart

@@ -14,7 +14,7 @@ Future<void> main() async {
 
     final String targetPlatform = await driver.requestData('getTargetPlatform');
 
-    Timeline timeline;
+    Timeline? timeline;
     switch (targetPlatform) {
       case 'TargetPlatform.iOS':
         {

dev/benchmarks/macrobenchmarks/test_driver/stack_size_perf_test.dart

@@ -16,7 +16,7 @@ const JsonEncoder _prettyEncoder = JsonEncoder.withIndent('  ');
 
 void main() {
   test('stack_size', () async {
-    int stackSizeInBytes;
+    late int stackSizeInBytes;
     await runDriverTestForRoute(kStackSizeRouteName, (FlutterDriver driver) async {
       final String stackSize = await driver.getText(find.byValueKey(kStackSizeKey));
       expect(stackSize.isNotEmpty, isTrue);

dev/benchmarks/macrobenchmarks/test_driver/util.dart

@@ -34,13 +34,13 @@ Future<void> runDriverTestForRoute(String routeName, DriverTestCallBack body) as
 void macroPerfTest(
   String testName,
   String routeName, {
-  Duration pageDelay,
+  Duration? pageDelay,
   Duration duration = const Duration(seconds: 3),
-  Future<void> Function(FlutterDriver driver) driverOps,
-  Future<void> Function(FlutterDriver driver) setupOps,
+  Future<void> Function(FlutterDriver driver)? driverOps,
+  Future<void> Function(FlutterDriver driver)? setupOps,
 }) {
   test(testName, () async {
-    Timeline timeline;
+    late Timeline timeline;
     await runDriverTestForRoute(routeName, (FlutterDriver driver) async {
       if (pageDelay != null) {
         // Wait for the page to load

dev/benchmarks/macrobenchmarks/test_memory/heavy_gridview.dart

@@ -10,8 +10,8 @@ import 'package:macrobenchmarks/main.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance.hasScheduledFrame);
+    await SchedulerBinding.instance!.endOfFrame;
+  } while (SchedulerBinding.instance!.hasScheduledFrame);
 }
 
 Future<void> main() async {

dev/benchmarks/macrobenchmarks/test_memory/large_images.dart

@@ -10,8 +10,8 @@ import 'package:macrobenchmarks/main.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance.hasScheduledFrame);
+    await SchedulerBinding.instance!.endOfFrame;
+  } while (SchedulerBinding.instance!.hasScheduledFrame);
 }
 
 Future<void> main() async {