make @immutable const classes (#9532)

* make @immutable const

* fix build

dev/benchmarks/complex_layout/lib/main.dart

@@ -24,7 +24,7 @@ class ComplexLayoutAppState extends State<ComplexLayoutApp> {
     return new MaterialApp(
       theme: lightTheme ? new ThemeData.light() : new ThemeData.dark(),
       title: 'Advanced Layout',
-      home: new ComplexLayout()
+      home: const ComplexLayout()
     );
   }
 
@@ -44,7 +44,7 @@ class ComplexLayoutAppState extends State<ComplexLayoutApp> {
 }
 
 class ComplexLayout extends StatefulWidget {
-  ComplexLayout({ Key key }) : super(key: key);
+  const ComplexLayout({ Key key }) : super(key: key);
 
   @override
   ComplexLayoutState createState() => new ComplexLayoutState();
@@ -85,7 +85,7 @@ class ComplexLayoutState extends State<ComplexLayout> {
           new BottomBar(),
         ],
       ),
-      drawer: new GalleryDrawer(),
+      drawer: const GalleryDrawer(),
     );
   }
 }
@@ -100,9 +100,9 @@ class TopBarMenu extends StatelessWidget {
           value: 'Friends',
           child: new MenuItemWithIcon(Icons.people, 'Friends', '5 new')
         ),
-        new PopupMenuItem<String>(
+        const PopupMenuItem<String>(
           value: 'Events',
-          child: new MenuItemWithIcon(Icons.event, 'Events', '12 upcoming')
+          child: const MenuItemWithIcon(Icons.event, 'Events', '12 upcoming')
         ),
         new PopupMenuItem<String>(
           value: 'Events',
@@ -120,9 +120,9 @@ class TopBarMenu extends StatelessWidget {
           value: 'Friends',
           child: new MenuItemWithIcon(Icons.people, 'Friends', '5')
         ),
-        new PopupMenuItem<String>(
+        const PopupMenuItem<String>(
           value: 'Events',
-          child: new MenuItemWithIcon(Icons.event, 'Events', '12')
+          child: const MenuItemWithIcon(Icons.event, 'Events', '12')
         ),
         new PopupMenuItem<String>(
           value: 'Events',
@@ -142,7 +142,7 @@ class TopBarMenu extends StatelessWidget {
 }
 
 class MenuItemWithIcon extends StatelessWidget {
-  MenuItemWithIcon(this.icon, this.title, this.subtitle);
+  const MenuItemWithIcon(this.icon, this.title, this.subtitle);
 
   final IconData icon;
   final String title;
@@ -164,7 +164,7 @@ class MenuItemWithIcon extends StatelessWidget {
 }
 
 class FancyImageItem extends StatelessWidget {
-  FancyImageItem(this.index, {Key key}) : super(key: key);
+  const FancyImageItem(this.index, {Key key}) : super(key: key);
 
   final int index;
 
@@ -188,14 +188,14 @@ class FancyImageItem extends StatelessWidget {
 }
 
 class FancyGalleryItem extends StatelessWidget {
-  FancyGalleryItem(this.index, {Key key}) : super(key: key);
+  const FancyGalleryItem(this.index, {Key key}) : super(key: key);
 
   final int index;
   @override
   Widget build(BuildContext context) {
     return new ListBody(
       children: <Widget>[
-        new UserHeader('Ali Connors'),
+        const UserHeader('Ali Connors'),
         new ItemGalleryBox(index),
         new InfoBar(),
         new Padding(
@@ -217,7 +217,7 @@ class InfoBar extends StatelessWidget {
       child: new Row(
         mainAxisAlignment: MainAxisAlignment.spaceBetween,
         children: <Widget>[
-          new MiniIconWithText(Icons.thumb_up, '42'),
+          const MiniIconWithText(Icons.thumb_up, '42'),
           new Text('3 Comments', style: Theme.of(context).textTheme.caption)
         ]
       )
@@ -233,9 +233,9 @@ class IconBar extends StatelessWidget {
       child: new Row(
         mainAxisAlignment: MainAxisAlignment.spaceBetween,
         children: <Widget>[
-          new IconWithText(Icons.thumb_up, 'Like'),
+          const IconWithText(Icons.thumb_up, 'Like'),
           new IconWithText(Icons.comment, 'Comment'),
-          new IconWithText(Icons.share, 'Share'),
+          const IconWithText(Icons.share, 'Share'),
         ]
       )
     );
@@ -243,7 +243,7 @@ class IconBar extends StatelessWidget {
 }
 
 class IconWithText extends StatelessWidget {
-  IconWithText(this.icon, this.title);
+  const IconWithText(this.icon, this.title);
 
   final IconData icon;
   final String title;
@@ -264,7 +264,7 @@ class IconWithText extends StatelessWidget {
 }
 
 class MiniIconWithText extends StatelessWidget {
-  MiniIconWithText(this.icon, this.title);
+  const MiniIconWithText(this.icon, this.title);
 
   final IconData icon;
   final String title;
@@ -305,7 +305,7 @@ class FatDivider extends StatelessWidget {
 }
 
 class UserHeader extends StatelessWidget {
-  UserHeader(this.userName);
+  const UserHeader(this.userName);
 
   final String userName;
 
@@ -443,7 +443,7 @@ class ItemImageBox extends StatelessWidget {
 }
 
 class ItemGalleryBox extends StatelessWidget {
-  ItemGalleryBox(this.index);
+  const ItemGalleryBox(this.index);
 
   final int index;
 
@@ -506,7 +506,7 @@ class ItemGalleryBox extends StatelessWidget {
               )
             ),
             new Container(
-              child: new TabPageSelector()
+              child: const TabPageSelector()
             )
           ]
         )
@@ -542,7 +542,7 @@ class BottomBar extends StatelessWidget {
 }
 
 class BottomBarButton extends StatelessWidget {
-  BottomBarButton(this.icon, this.title);
+  const BottomBarButton(this.icon, this.title);
 
   final IconData icon;
   final String title;
@@ -565,7 +565,7 @@ class BottomBarButton extends StatelessWidget {
 }
 
 class GalleryDrawer extends StatelessWidget {
-  GalleryDrawer({ Key key }) : super(key: key);
+  const GalleryDrawer({ Key key }) : super(key: key);
 
   void _changeTheme(BuildContext context, bool value) {
     ComplexLayoutApp.of(context).lightTheme = value;

dev/manual_tests/drag_and_drop.dart

@@ -74,7 +74,7 @@ class DotState extends State<Dot> {
 }
 
 class ExampleDragSource extends StatelessWidget {
-  ExampleDragSource({
+  const ExampleDragSource({
     Key key,
     this.color,
     this.heavy: false,
@@ -174,7 +174,7 @@ class DashOutlineCirclePainter extends CustomPainter {
 }
 
 class MovableBall extends StatelessWidget {
-  MovableBall(this.position, this.ballPosition, this.callback);
+  const MovableBall(this.position, this.ballPosition, this.callback);
 
   final int position;
   final int ballPosition;

dev/manual_tests/material_arc.dart

@@ -103,7 +103,7 @@ class _PointDemoPainter extends CustomPainter {
 }
 
 class _PointDemo extends StatefulWidget {
-  _PointDemo({ Key key, this.controller }) : super(key: key);
+  const _PointDemo({ Key key, this.controller }) : super(key: key);
 
   final AnimationController controller;
 
@@ -268,7 +268,7 @@ class _RectangleDemoPainter extends CustomPainter {
 }
 
 class _RectangleDemo extends StatefulWidget {
-  _RectangleDemo({ Key key, this.controller }) : super(key: key);
+  const _RectangleDemo({ Key key, this.controller }) : super(key: key);
 
   final AnimationController controller;
 
@@ -404,7 +404,7 @@ class _ArcDemo {
 }
 
 class AnimationDemo extends StatefulWidget {
-  AnimationDemo({ Key key }) : super(key: key);
+  const AnimationDemo({ Key key }) : super(key: key);
 
   @override
   _AnimationDemoState createState() => new _AnimationDemoState();
@@ -469,6 +469,6 @@ class _AnimationDemoState extends State<AnimationDemo> with TickerProviderStateM
 
 void main() {
   runApp(new MaterialApp(
-    home: new AnimationDemo()
+    home: const AnimationDemo()
   ));
 }

dev/manual_tests/overlay_geometry.dart

@@ -57,7 +57,7 @@ class _MarkerPainter extends CustomPainter {
 }
 
 class Marker extends StatelessWidget {
-  Marker({
+  const Marker({
     Key key,
     this.type: MarkerType.touch,
     this.position,

dev/manual_tests/raw_keyboard.dart

@@ -12,15 +12,15 @@ void main() {
       appBar: new AppBar(
         title: const Text('Hardware Key Demo'),
       ),
-      body: new Center(
-        child: new RawKeyboardDemo(),
+      body: const Center(
+        child: const RawKeyboardDemo(),
       ),
     ),
   ));
 }
 
 class RawKeyboardDemo extends StatefulWidget {
-  RawKeyboardDemo({ Key key }) : super(key: key);
+  const RawKeyboardDemo({ Key key }) : super(key: key);
 
   @override
   _HardwareKeyDemoState createState() => new _HardwareKeyDemoState();

examples/flutter_gallery/lib/demo/animation/home.dart

@@ -366,7 +366,7 @@ class _AllSectionsView extends AnimatedWidget {
 }
 
 class AnimationDemoHome extends StatefulWidget {
-  AnimationDemoHome({ Key key }) : super(key: key);
+  const AnimationDemoHome({ Key key }) : super(key: key);
 
   static const String routeName = '/animation';
 

examples/flutter_gallery/lib/demo/animation/widgets.dart

@@ -100,7 +100,7 @@ class SectionTitle extends StatelessWidget {
 
 // Small horizontal bar that indicates the selected section.
 class SectionIndicator extends StatelessWidget {
-  SectionIndicator({ Key key, this.opacity: 1.0 }) : super(key: key);
+  const SectionIndicator({ Key key, this.opacity: 1.0 }) : super(key: key);
 
   final double opacity;
 

examples/flutter_gallery/lib/demo/animation_demo.dart

@@ -7,10 +7,10 @@ import 'package:flutter/material.dart';
 import 'animation/home.dart';
 
 class AnimationDemo extends StatelessWidget {
-  AnimationDemo({Key key}) : super(key: key);
+  const AnimationDemo({Key key}) : super(key: key);
 
   static const String routeName = '/animation';
 
   @override
-  Widget build(BuildContext context) => new AnimationDemoHome();
+  Widget build(BuildContext context) => const AnimationDemoHome();
 }

examples/flutter_gallery/lib/demo/calculator/home.dart

@@ -7,7 +7,7 @@ import 'package:flutter/material.dart';
 import 'logic.dart';
 
 class Calculator extends StatefulWidget {
-  Calculator({Key key}) : super(key: key);
+  const Calculator({Key key}) : super(key: key);
 
   @override
   _CalculatorState createState() => new _CalculatorState();
@@ -138,7 +138,7 @@ class _CalculatorState extends State<Calculator> {
 }
 
 class CalcDisplay extends StatelessWidget {
-  CalcDisplay({ this.content });
+  const CalcDisplay({ this.content });
 
   final String content;
 
@@ -154,7 +154,7 @@ class CalcDisplay extends StatelessWidget {
 }
 
 class KeyPad extends StatelessWidget {
-  KeyPad({ this.calcState });
+  const KeyPad({ this.calcState });
 
   final _CalculatorState calcState;
 
@@ -222,7 +222,7 @@ class KeyPad extends StatelessWidget {
 }
 
 class KeyRow extends StatelessWidget {
-  KeyRow(this.keys);
+  const KeyRow(this.keys);
 
   final List<Widget> keys;
 
@@ -238,7 +238,7 @@ class KeyRow extends StatelessWidget {
 }
 
 class CalcKey extends StatelessWidget {
-  CalcKey(this.text, this.onTap);
+  const CalcKey(this.text, this.onTap);
 
   final String text;
   final GestureTapCallback onTap;

examples/flutter_gallery/lib/demo/calculator_demo.dart

@@ -7,10 +7,10 @@ import 'package:flutter/material.dart';
 import 'calculator/home.dart';
 
 class CalculatorDemo extends StatelessWidget {
-  CalculatorDemo({Key key}) : super(key: key);
+  const CalculatorDemo({Key key}) : super(key: key);
 
   static const String routeName = '/calculator';
 
   @override
-  Widget build(BuildContext context) => new Calculator();
+  Widget build(BuildContext context) => const Calculator();
 }

examples/flutter_gallery/lib/demo/contacts_demo.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class _ContactCategory extends StatelessWidget {
-  _ContactCategory({ Key key, this.icon, this.children }) : super(key: key);
+  const _ContactCategory({ Key key, this.icon, this.children }) : super(key: key);
 
   final IconData icon;
   final List<Widget> children;

examples/flutter_gallery/lib/demo/material/buttons_demo.dart

@@ -100,7 +100,7 @@ class _ButtonsDemoState extends State<ButtonsDemo> {
               // Perform some action
             },
           ),
-          new RaisedButton(
+          const RaisedButton(
             child: const Text('DISABLED'),
             onPressed: null,
           )

examples/flutter_gallery/lib/demo/material/chip_demo.dart

@@ -26,8 +26,8 @@ class _ChipDemoState extends State<ChipDemo> {
       const Chip(
         label: const Text('Apple')
       ),
-      new Chip(
-        avatar: new CircleAvatar(child: const Text('B')),
+      const Chip(
+        avatar: const CircleAvatar(child: const Text('B')),
         label: const Text('Blueberry')
       ),
     ];

examples/flutter_gallery/lib/demo/material/date_and_time_picker_demo.dart

@@ -8,7 +8,7 @@ import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
 
 class _InputDropdown extends StatelessWidget {
-  _InputDropdown({
+  const _InputDropdown({
     Key key,
     this.child,
     this.labelText,
@@ -47,7 +47,7 @@ class _InputDropdown extends StatelessWidget {
 }
 
 class _DateTimePicker extends StatelessWidget {
-  _DateTimePicker({
+  const _DateTimePicker({
     Key key,
     this.labelText,
     this.selectedDate,

examples/flutter_gallery/lib/demo/material/dialog_demo.dart

@@ -20,7 +20,7 @@ const String _alertWithTitleText =
   "data to Google, even when no apps are running.";
 
 class DialogDemoItem extends StatelessWidget {
-  DialogDemoItem({ Key key, this.icon, this.color, this.text, this.onPressed }) : super(key: key);
+  const DialogDemoItem({ Key key, this.icon, this.color, this.text, this.onPressed }) : super(key: key);
 
   final IconData icon;
   final Color color;

examples/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

@@ -14,7 +14,7 @@ typedef Widget DemoItemBodyBuilder<T>(DemoItem<T> item);
 typedef String ValueToString<T>(T value);
 
 class DualHeaderWithHint extends StatelessWidget {
-  DualHeaderWithHint({
+  const DualHeaderWithHint({
     this.name,
     this.value,
     this.hint,
@@ -76,7 +76,7 @@ class DualHeaderWithHint extends StatelessWidget {
 }
 
 class CollapsibleBody extends StatelessWidget {
-  CollapsibleBody({
+  const CollapsibleBody({
     this.margin: EdgeInsets.zero,
     this.child,
     this.onSave,

examples/flutter_gallery/lib/demo/material/grid_list_demo.dart

@@ -29,7 +29,7 @@ class Photo {
 }
 
 class GridPhotoViewer extends StatefulWidget {
-  GridPhotoViewer({ Key key, this.photo }) : super(key: key);
+  const GridPhotoViewer({ Key key, this.photo }) : super(key: key);
 
   final Photo photo;
 
@@ -38,7 +38,7 @@ class GridPhotoViewer extends StatefulWidget {
 }
 
 class _GridTitleText extends StatelessWidget {
-  _GridTitleText(this.text);
+  const _GridTitleText(this.text);
 
   final String text;
 
@@ -227,7 +227,7 @@ class GridDemoPhotoItem extends StatelessWidget {
 }
 
 class GridListDemo extends StatefulWidget {
-  GridListDemo({ Key key }) : super(key: key);
+  const GridListDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/grid-list';
 

examples/flutter_gallery/lib/demo/material/leave_behind_demo.dart

@@ -29,7 +29,7 @@ class LeaveBehindItem implements Comparable<LeaveBehindItem> {
 }
 
 class LeaveBehindDemo extends StatefulWidget {
-  LeaveBehindDemo({ Key key }) : super(key: key);
+  const LeaveBehindDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/leave-behind';
 

examples/flutter_gallery/lib/demo/material/list_demo.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class ListDemo extends StatefulWidget {
-  ListDemo({ Key key }) : super(key: key);
+  const ListDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/list';
 

examples/flutter_gallery/lib/demo/material/menu_demo.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class MenuDemo extends StatefulWidget {
-  MenuDemo({ Key key }) : super(key: key);
+  const MenuDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/menu';
 

examples/flutter_gallery/lib/demo/material/overscroll_demo.dart

@@ -9,7 +9,7 @@ import 'package:flutter/material.dart';
 enum IndicatorType { overscroll, refresh }
 
 class OverscrollDemo extends StatefulWidget {
-  OverscrollDemo({ Key key }) : super(key: key);
+  const OverscrollDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/overscroll';
 

examples/flutter_gallery/lib/demo/material/page_selector_demo.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class _PageSelector extends StatelessWidget {
-  _PageSelector({ this.icons });
+  const _PageSelector({ this.icons });
 
   final List<IconData> icons;
 

examples/flutter_gallery/lib/demo/material/selection_controls_demo.dart

@@ -98,8 +98,8 @@ class _SelectionControlsDemoState extends State<SelectionControlsDemo> {
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
               // Disabled checkboxes
-              new Checkbox(value: true, onChanged: null),
-              new Checkbox(value: false, onChanged: null)
+              const Checkbox(value: true, onChanged: null),
+              const Checkbox(value: false, onChanged: null)
             ]
           )
         ]
@@ -137,17 +137,17 @@ class _SelectionControlsDemoState extends State<SelectionControlsDemo> {
           new Row(
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
-              new Radio<int>(
+              const Radio<int>(
                 value: 0,
                 groupValue: 0,
                 onChanged: null
               ),
-              new Radio<int>(
+              const Radio<int>(
                 value: 1,
                 groupValue: 0,
                 onChanged: null
               ),
-              new Radio<int>(
+              const Radio<int>(
                 value: 2,
                 groupValue: 0,
                 onChanged: null

examples/flutter_gallery/lib/demo/material/snack_bar_demo.dart

@@ -17,7 +17,7 @@ const String _text3 =
   "By default snackbars automatically disappear after a few seconds ";
 
 class SnackBarDemo extends StatefulWidget {
-  SnackBarDemo({ Key key }) : super(key: key);
+  const SnackBarDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/snack-bar';
 

examples/flutter_gallery/lib/demo/material/tabs_demo.dart

@@ -75,7 +75,7 @@ final Map<_Page, List<_CardData>> _allPages = <_Page, List<_CardData>>{
 };
 
 class _CardDataItem extends StatelessWidget {
-  _CardDataItem({ this.page, this.data });
+  const _CardDataItem({ this.page, this.data });
 
   static final double height = 272.0;
   final _Page page;

examples/flutter_gallery/lib/demo/material/text_form_field_demo.dart

@@ -7,7 +7,7 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 
 class TextFormFieldDemo extends StatefulWidget {
-  TextFormFieldDemo({ Key key }) : super(key: key);
+  const TextFormFieldDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/text-form-field';
 

examples/flutter_gallery/lib/demo/pesto_demo.dart

@@ -6,7 +6,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
 class PestoDemo extends StatelessWidget {
-  PestoDemo({ Key key }) : super(key: key);
+  const PestoDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/pesto';
 
@@ -31,7 +31,7 @@ final ThemeData _kTheme = new ThemeData(
 class PestoHome extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    return new RecipeGridPage(recipes: kPestoRecipes);
+    return const RecipeGridPage(recipes: kPestoRecipes);
   }
 }
 
@@ -63,7 +63,7 @@ class PestoStyle extends TextStyle {
 
 // Displays a grid of recipe cards.
 class RecipeGridPage extends StatefulWidget {
-  RecipeGridPage({ Key key, this.recipes }) : super(key: key);
+  const RecipeGridPage({ Key key, this.recipes }) : super(key: key);
 
   final List<Recipe> recipes;
 
@@ -180,7 +180,7 @@ class _RecipeGridPageState extends State<RecipeGridPage> {
 }
 
 class PestoLogo extends StatefulWidget {
-  PestoLogo({this.height, this.t});
+  const PestoLogo({this.height, this.t});
 
   final double height;
   final double t;
@@ -239,7 +239,7 @@ class RecipeCard extends StatelessWidget {
   final TextStyle titleStyle = const PestoStyle(fontSize: 24.0, fontWeight: FontWeight.w600);
   final TextStyle authorStyle = const PestoStyle(fontWeight: FontWeight.w500, color: Colors.black54);
 
-  RecipeCard({ Key key, this.recipe, this.onTap }) : super(key: key);
+  const RecipeCard({ Key key, this.recipe, this.onTap }) : super(key: key);
 
   final Recipe recipe;
   final VoidCallback onTap;
@@ -289,7 +289,7 @@ class RecipeCard extends StatelessWidget {
 
 // Displays one recipe. Includes the recipe sheet with a background image.
 class RecipePage extends StatefulWidget {
-  RecipePage({ Key key, this.recipe }) : super(key: key);
+  const RecipePage({ Key key, this.recipe }) : super(key: key);
 
   final Recipe recipe;
 

examples/flutter_gallery/lib/demo/shrine/shrine_home.dart

@@ -148,9 +148,9 @@ class _VendorItem extends StatelessWidget {
 // Displays the product's price. If the product is in the shopping cart then the
 // background is highlighted.
 abstract class _PriceItem extends StatelessWidget {
-  _PriceItem({ Key key, @required this.product }) : super(key: key) {
-    assert(product != null);
-  }
+  const _PriceItem({ Key key, @required this.product })
+      : assert(product != null),
+        super(key: key);
 
   final Product product;
 
@@ -168,7 +168,7 @@ abstract class _PriceItem extends StatelessWidget {
 }
 
 class _ProductPriceItem extends _PriceItem {
-  _ProductPriceItem({ Key key, Product product }) : super(key: key, product: product);
+  const _ProductPriceItem({ Key key, Product product }) : super(key: key, product: product);
 
   @override
   Widget build(BuildContext context) {
@@ -181,7 +181,7 @@ class _ProductPriceItem extends _PriceItem {
 }
 
 class _FeaturePriceItem extends _PriceItem {
-  _FeaturePriceItem({ Key key, Product product }) : super(key: key, product: product);
+  const _FeaturePriceItem({ Key key, Product product }) : super(key: key, product: product);
 
   @override
   Widget build(BuildContext context) {

examples/flutter_gallery/lib/gallery/app.dart

@@ -32,7 +32,7 @@ final ThemeData _kGalleryDarkTheme = new ThemeData(
 );
 
 class GalleryApp extends StatefulWidget {
-  GalleryApp({
+  const GalleryApp({
     this.updateUrlFetcher,
     this.enablePerformanceOverlay: true,
     this.checkerboardRasterCacheImages: true,

examples/flutter_gallery/lib/gallery/demo.dart

@@ -33,7 +33,7 @@ class ComponentDemoTabData {
 }
 
 class TabbedComponentDemoScaffold extends StatelessWidget {
-  TabbedComponentDemoScaffold({
+  const TabbedComponentDemoScaffold({
     this.title,
     this.demos
   });
@@ -96,7 +96,7 @@ class TabbedComponentDemoScaffold extends StatelessWidget {
 }
 
 class FullScreenCodeDialog extends StatefulWidget {
-  FullScreenCodeDialog({ this.exampleCodeTag });
+  const FullScreenCodeDialog({ this.exampleCodeTag });
 
   final String exampleCodeTag;
 

examples/flutter_gallery/lib/gallery/example_code.dart

@@ -25,7 +25,7 @@ new RaisedButton(
 // Create a disabled button.
 // Buttons are disabled when onPressed isn't
 // specified or is null.
-new RaisedButton(
+const RaisedButton(
   child: const Text('BUTTON TITLE'),
   onPressed: null
 );
@@ -130,7 +130,7 @@ new Checkbox(
 // Create a disabled checkbox.
 // Checkboxes are disabled when onChanged isn't
 // specified or null.
-new Checkbox(value: false, onChanged: null);
+const Checkbox(value: false, onChanged: null);
 // END
 
 
@@ -167,7 +167,7 @@ new Row(
 );
 
 // Creates a disabled radio button.
-new Radio<int>(
+const Radio<int>(
   value: 0,
   groupValue: 0,
   onChanged: null

examples/flutter_gallery/lib/gallery/home.dart

@@ -36,7 +36,7 @@ final List<_BackgroundLayer> _kBackgroundLayers = <_BackgroundLayer>[
 ];
 
 class _AppBarBackground extends StatelessWidget {
-  _AppBarBackground({ Key key, this.animation }) : super(key: key);
+  const _AppBarBackground({ Key key, this.animation }) : super(key: key);
 
   final Animation<double> animation;
 

examples/flutter_gallery/lib/gallery/item.dart

@@ -73,7 +73,7 @@ List<GalleryItem> _buildGalleryItems() {
       subtitle: 'Section organizer',
       category: 'Demos',
       routeName: AnimationDemo.routeName,
-      buildRoute: (BuildContext context) => new AnimationDemo(),
+      buildRoute: (BuildContext context) => const AnimationDemo(),
     ),
     // Material Components
     new GalleryItem(
@@ -151,7 +151,7 @@ List<GalleryItem> _buildGalleryItems() {
       subtitle: 'Row and column layout',
       category: 'Material Components',
       routeName: GridListDemo.routeName,
-      buildRoute: (BuildContext context) => new GridListDemo(),
+      buildRoute: (BuildContext context) => const GridListDemo(),
     ),
     new GalleryItem(
       title: 'Icons',
@@ -165,21 +165,21 @@ List<GalleryItem> _buildGalleryItems() {
       subtitle: 'List items with hidden actions',
       category: 'Material Components',
       routeName: LeaveBehindDemo.routeName,
-      buildRoute: (BuildContext context) => new LeaveBehindDemo(),
+      buildRoute: (BuildContext context) => const LeaveBehindDemo(),
     ),
     new GalleryItem(
       title: 'List',
       subtitle: 'Layout variations for scrollable lists',
       category: 'Material Components',
       routeName: ListDemo.routeName,
-      buildRoute: (BuildContext context) => new ListDemo(),
+      buildRoute: (BuildContext context) => const ListDemo(),
     ),
     new GalleryItem(
       title: 'Menus',
       subtitle: 'Menu buttons and simple menus',
       category: 'Material Components',
       routeName: MenuDemo.routeName,
-      buildRoute: (BuildContext context) => new MenuDemo(),
+      buildRoute: (BuildContext context) => const MenuDemo(),
     ),
     new GalleryItem(
       title: 'Modal bottom sheet',
@@ -214,7 +214,7 @@ List<GalleryItem> _buildGalleryItems() {
       subtitle: 'Refresh indicators',
       category: 'Material Components',
       routeName: OverscrollDemo.routeName,
-      buildRoute: (BuildContext context) => new OverscrollDemo(),
+      buildRoute: (BuildContext context) => const OverscrollDemo(),
     ),
     new GalleryItem(
       title: 'Scrollable tabs',
@@ -242,7 +242,7 @@ List<GalleryItem> _buildGalleryItems() {
       subtitle: 'Temporary message that appears at the bottom',
       category: 'Material Components',
       routeName: SnackBarDemo.routeName,
-      buildRoute: (BuildContext context) => new SnackBarDemo(),
+      buildRoute: (BuildContext context) => const SnackBarDemo(),
     ),
     new GalleryItem(
       title: 'Tabs',
@@ -256,7 +256,7 @@ List<GalleryItem> _buildGalleryItems() {
       subtitle: 'Single line of editable text and numbers',
       category: 'Material Components',
       routeName: TextFormFieldDemo.routeName,
-      buildRoute: (BuildContext context) => new TextFormFieldDemo(),
+      buildRoute: (BuildContext context) => const TextFormFieldDemo(),
     ),
     new GalleryItem(
       title: 'Tooltips',
@@ -327,7 +327,7 @@ List<GalleryItem> _buildGalleryItems() {
         subtitle: 'Simple recipe browser',
         category: 'Demos',
         routeName: PestoDemo.routeName,
-        buildRoute: (BuildContext context) => new PestoDemo(),
+        buildRoute: (BuildContext context) => const PestoDemo(),
       ),
     );
     return true;

examples/flutter_gallery/lib/main.dart

@@ -10,5 +10,5 @@ import 'package:flutter/widgets.dart';
 import 'gallery/app.dart';
 
 void main() {
-  runApp(new GalleryApp());
+  runApp(const GalleryApp());
 }

examples/flutter_gallery/test/calculator/smoke_test.dart

@@ -14,7 +14,7 @@ void main() {
   // We press the "1" and the "2" buttons and check that the display
   // reads "12".
   testWidgets('Flutter calculator app smoke test', (WidgetTester tester)  async {
-    await tester.pumpWidget(new CalculatorDemo());
+    await tester.pumpWidget(const CalculatorDemo());
 
     final Finder oneButton = find.widgetWithText(InkResponse, '1');
     expect(oneButton, findsOneWidget);

examples/flutter_gallery/test/example_code_display_test.dart

@@ -14,7 +14,7 @@ void main() {
   testWidgets('Flutter gallery button example code displays', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/6147
 
-    await tester.pumpWidget(new GalleryApp());
+    await tester.pumpWidget(const GalleryApp());
     await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
     await tester.pump(); // triggers a frame
 

examples/flutter_gallery/test/pesto_test.dart

@@ -15,11 +15,11 @@ void main() {
   testWidgets('Pesto appbar heroics', (WidgetTester tester) async {
     await tester.pumpWidget(
       // The bug only manifests itself when the screen's orientation is portrait
-      new Center(
-        child: new SizedBox(
+      const Center(
+        child: const SizedBox(
           width: 400.0,
           height: 800.0,
-          child: new GalleryApp()
+          child: const GalleryApp()
         )
       )
     );
@@ -43,7 +43,7 @@ void main() {
   });
 
   testWidgets('Pesto can be scrolled all the way down', (WidgetTester tester) async {
-    await tester.pumpWidget(new GalleryApp());
+    await tester.pumpWidget(const GalleryApp());
     await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
 
     await tester.tap(find.text('Pesto'));

examples/flutter_gallery/test/update_test.dart

@@ -17,7 +17,7 @@ void main() {
 
   // Regression test for https://github.com/flutter/flutter/pull/5168
   testWidgets('update dialog', (WidgetTester tester) async {
-    await tester.pumpWidget(new GalleryApp(updateUrlFetcher: mockUpdateUrlFetcher));
+    await tester.pumpWidget(const GalleryApp(updateUrlFetcher: mockUpdateUrlFetcher));
     await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
     await tester.pump(); // triggers a frame
 

examples/layers/widgets/custom_render_box.dart

@@ -39,12 +39,12 @@ class RenderDots extends RenderConstrainedBox {
 }
 
 class Dots extends SingleChildRenderObjectWidget {
-  Dots({ Key key, Widget child }) : super(key: key, child: child);
+  const Dots({ Key key, Widget child }) : super(key: key, child: child);
 
   @override
   RenderDots createRenderObject(BuildContext context) => new RenderDots();
 }
 
 void main() {
-  runApp(new Dots(child: const Center(child: const Text('Touch me!'))));
+  runApp(const Dots(child: const Center(child: const Text('Touch me!'))));
 }

examples/layers/widgets/media_query.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 
 class AdaptedListItem extends StatelessWidget {
-  AdaptedListItem({ Key key, this.name }) : super(key: key);
+  const AdaptedListItem({ Key key, this.name }) : super(key: key);
 
   final String name;
 
@@ -28,7 +28,7 @@ class AdaptedListItem extends StatelessWidget {
 }
 
 class AdaptedGridItem extends StatelessWidget {
-  AdaptedGridItem({ Key key, this.name }) : super(key: key);
+  const AdaptedGridItem({ Key key, this.name }) : super(key: key);
 
   final String name;
 
@@ -69,7 +69,7 @@ const double _kMaxTileWidth = 150.0;
 const double _kGridViewBreakpoint = 450.0;
 
 class AdaptiveContainer extends StatelessWidget {
-  AdaptiveContainer({ Key key, this.names }) : super(key: key);
+  const AdaptiveContainer({ Key key, this.names }) : super(key: key);
 
   final List<String> names;
 

examples/layers/widgets/spinning_mixed.dart

@@ -17,7 +17,7 @@ void addFlexChildSolidColor(RenderFlex parent, Color backgroundColor, { int flex
 
 // Solid colour, Widget version
 class Rectangle extends StatelessWidget {
-  Rectangle(this.color, { Key key }) : super(key: key);
+  const Rectangle(this.color, { Key key }) : super(key: key);
 
   final Color color;
 
@@ -41,7 +41,7 @@ void attachWidgetTreeToRenderTree(RenderProxyBox container) {
       height: 300.0,
       child: new Column(
         children: <Widget>[
-          new Rectangle(const Color(0xFF00FFFF)),
+          const Rectangle(const Color(0xFF00FFFF)),
           new Material(
             child: new Container(
               padding: const EdgeInsets.all(10.0),
@@ -66,7 +66,7 @@ void attachWidgetTreeToRenderTree(RenderProxyBox container) {
               )
             )
           ),
-          new Rectangle(const Color(0xFFFFFF00)),
+          const Rectangle(const Color(0xFFFFFF00)),
         ],
         mainAxisAlignment: MainAxisAlignment.spaceBetween
       )

examples/stocks/lib/stock_arrow.dart

@@ -53,7 +53,7 @@ class StockArrowPainter extends CustomPainter {
 }
 
 class StockArrow extends StatelessWidget {
-  StockArrow({ Key key, this.percentChange }) : super(key: key);
+  const StockArrow({ Key key, this.percentChange }) : super(key: key);
 
   final double percentChange;
 

examples/stocks/lib/stock_home.dart

@@ -345,7 +345,7 @@ class _CreateCompanySheet extends StatelessWidget {
     // TODO(ianh): Fill this out.
     return new Column(
       children: <Widget>[
-        new TextField(
+        const TextField(
           autofocus: true,
           decoration: const InputDecoration(
             hintText: 'Company Name',

examples/stocks/lib/stock_list.dart

@@ -8,7 +8,7 @@ import 'stock_data.dart';
 import 'stock_row.dart';
 
 class StockList extends StatelessWidget {
-  StockList({ Key key, this.stocks, this.onOpen, this.onShow, this.onAction }) : super(key: key);
+  const StockList({ Key key, this.stocks, this.onOpen, this.onShow, this.onAction }) : super(key: key);
 
   final List<Stock> stocks;
   final StockRowActionCallback onOpen;

examples/stocks/lib/stock_symbol_viewer.dart

@@ -8,7 +8,7 @@ import 'stock_arrow.dart';
 import 'stock_data.dart';
 
 class _StockSymbolView extends StatelessWidget {
-  _StockSymbolView({ this.stock, this.arrow });
+  const _StockSymbolView({ this.stock, this.arrow });
 
   final Stock stock;
   final Widget arrow;
@@ -63,7 +63,7 @@ class _StockSymbolView extends StatelessWidget {
 }
 
 class StockSymbolPage extends StatelessWidget {
-  StockSymbolPage({ this.stock });
+  const StockSymbolPage({ this.stock });
 
   final Stock stock;
 
@@ -92,7 +92,7 @@ class StockSymbolPage extends StatelessWidget {
 }
 
 class StockSymbolBottomSheet extends StatelessWidget {
-  StockSymbolBottomSheet({ this.stock });
+  const StockSymbolBottomSheet({ this.stock });
 
   final Stock stock;
 

packages/flutter/lib/src/cupertino/dialog.dart

@@ -57,7 +57,7 @@ const BoxDecoration _kCupertinoDialogDecoration = const BoxDecoration(
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/ui-views/alerts/>
 class CupertinoDialog extends StatelessWidget {
   /// Creates an iOS-style dialog.
-  CupertinoDialog({
+  const CupertinoDialog({
     Key key,
     this.child,
   }) : super(key: key);
@@ -94,7 +94,7 @@ class CupertinoDialog extends StatelessWidget {
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/ui-views/alerts/>
 class CupertinoAlertDialog extends StatelessWidget {
   /// Creates an iOS-style alert dialog.
-  CupertinoAlertDialog({
+  const CupertinoAlertDialog({
     Key key,
     this.title,
     this.content,
@@ -233,7 +233,7 @@ const double _kButtonBarHeight = 45.0;
 const Color _kButtonDividerColor = const Color(0xFFD5D5D5);
 
 class _CupertinoButtonBar extends StatelessWidget {
-  _CupertinoButtonBar({
+  const _CupertinoButtonBar({
     Key key,
     this.children,
   }) : super(key: key);

packages/flutter/lib/src/cupertino/slider.dart

@@ -140,7 +140,7 @@ class _CupertinoSliderState extends State<CupertinoSlider> with TickerProviderSt
 }
 
 class _CupertinoSliderRenderObjectWidget extends LeafRenderObjectWidget {
-  _CupertinoSliderRenderObjectWidget({
+  const _CupertinoSliderRenderObjectWidget({
     Key key,
     this.value,
     this.divisions,

packages/flutter/lib/src/cupertino/switch.dart

@@ -26,7 +26,7 @@ import 'thumb_painter.dart';
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/ui-controls/switches/>
 class CupertinoSwitch extends StatefulWidget {
   /// Creates an iOS-style switch.
-  CupertinoSwitch({
+  const CupertinoSwitch({
     Key key,
     @required this.value,
     @required this.onChanged,
@@ -88,7 +88,7 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
 }
 
 class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
-  _CupertinoSwitchRenderObjectWidget({
+  const _CupertinoSwitchRenderObjectWidget({
     Key key,
     this.value,
     this.activeColor,

packages/flutter/lib/src/material/about.dart

@@ -39,7 +39,7 @@ class AboutListTile extends StatelessWidget {
   /// The arguments are all optional. The application name, if omitted, will be
   /// derived from the nearest [Title] widget. The version, icon, and legalese
   /// values default to the empty string.
-  AboutListTile({
+  const AboutListTile({
     Key key,
     this.icon: const Icon(null),
     this.child,
@@ -210,7 +210,7 @@ class AboutDialog extends StatelessWidget {
   /// The arguments are all optional. The application name, if omitted, will be
   /// derived from the nearest [Title] widget. The version, icon, and legalese
   /// values default to the empty string.
-  AboutDialog({
+  const AboutDialog({
     Key key,
     this.applicationName,
     this.applicationVersion,

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -171,7 +171,7 @@ class _ModalBottomSheetLayout extends SingleChildLayoutDelegate {
 }
 
 class _ModalBottomSheet<T> extends StatefulWidget {
-  _ModalBottomSheet({ Key key, this.route }) : super(key: key);
+  const _ModalBottomSheet({ Key key, this.route }) : super(key: key);
 
   final _ModalBottomSheetRoute<T> route;
 

packages/flutter/lib/src/material/button.dart

@@ -126,7 +126,7 @@ class MaterialButton extends StatefulWidget {
   ///
   /// Rather than creating a material button directly, consider using
   /// [FlatButton] or [RaisedButton].
-  MaterialButton({
+  const MaterialButton({
     Key key,
     this.colorBrightness,
     this.textTheme,

packages/flutter/lib/src/material/button_bar.dart

@@ -27,7 +27,7 @@ class ButtonBar extends StatelessWidget {
   /// Creates a button bar.
   ///
   /// The alignment argument defaults to [MainAxisAlignment.end].
-  ButtonBar({
+  const ButtonBar({
     Key key,
     this.alignment: MainAxisAlignment.end,
     this.mainAxisSize: MainAxisSize.max,

packages/flutter/lib/src/material/checkbox.dart

@@ -41,7 +41,7 @@ class Checkbox extends StatefulWidget {
   ///
   /// * [value] determines whether the checkbox is checked.
   /// * [onChanged] is called when the value of the checkbox should change.
-  Checkbox({
+  const Checkbox({
     Key key,
     @required this.value,
     @required this.onChanged,

packages/flutter/lib/src/material/circle_avatar.dart

@@ -44,7 +44,7 @@ import 'typography.dart';
 ///  * <https://material.google.com/components/chips.html#chips-contact-chips>
 class CircleAvatar extends StatelessWidget {
   /// Creates a circle that represents a user.
-  CircleAvatar({
+  const CircleAvatar({
     Key key,
     this.child,
     this.backgroundColor,

packages/flutter/lib/src/material/data_table.dart

@@ -607,7 +607,7 @@ class DataTable extends StatelessWidget {
 /// [Table], and put the other contents of the cell inside it.)
 class TableRowInkWell extends InkResponse {
   /// Creates an ink well for a table row.
-  TableRowInkWell({
+  const TableRowInkWell({
     Key key,
     Widget child,
     GestureTapCallback onTap,
@@ -661,7 +661,7 @@ class TableRowInkWell extends InkResponse {
 }
 
 class _SortArrow extends StatefulWidget {
-  _SortArrow({
+  const _SortArrow({
     Key key,
     this.visible,
     this.down,

packages/flutter/lib/src/material/date_picker.dart

@@ -573,7 +573,7 @@ class _YearPickerState extends State<YearPicker> {
 }
 
 class _DatePickerDialog extends StatefulWidget {
-  _DatePickerDialog({
+  const _DatePickerDialog({
     Key key,
     this.initialDate,
     this.firstDate,

packages/flutter/lib/src/material/dialog.dart

@@ -31,7 +31,7 @@ class Dialog extends StatelessWidget {
   /// Creates a dialog.
   ///
   /// Typically used in conjunction with [showDialog].
-  Dialog({
+  const Dialog({
     Key key,
     this.child,
   }) : super(key: key);
@@ -90,7 +90,7 @@ class AlertDialog extends StatelessWidget {
   /// Creates an alert dialog.
   ///
   /// Typically used in conjunction with [showDialog].
-  AlertDialog({
+  const AlertDialog({
     Key key,
     this.title,
     this.titlePadding,
@@ -194,7 +194,7 @@ class AlertDialog extends StatelessWidget {
 ///  * <https://material.google.com/components/dialogs.html#dialogs-simple-dialogs>
 class SimpleDialogOption extends StatelessWidget {
   /// Creates an option for a [SimpleDialog].
-  SimpleDialogOption({
+  const SimpleDialogOption({
     Key key,
     this.onPressed,
     this.child,
@@ -244,7 +244,7 @@ class SimpleDialog extends StatelessWidget {
   /// Creates a simple dialog.
   ///
   /// Typically used in conjunction with [showDialog].
-  SimpleDialog({
+  const SimpleDialog({
     Key key,
     this.title,
     this.titlePadding,

packages/flutter/lib/src/material/drawer.dart

@@ -66,7 +66,7 @@ class Drawer extends StatelessWidget {
   /// Creates a material design drawer.
   ///
   /// Typically used in the [Scaffold.drawer] property.
-  Drawer({
+  const Drawer({
     Key key,
     this.elevation: 16,
     this.child

packages/flutter/lib/src/material/dropdown.dart

@@ -90,7 +90,7 @@ class _DropdownScrollBehavior extends ScrollBehavior {
 }
 
 class _DropdownMenu<T> extends StatefulWidget {
-  _DropdownMenu({
+  const _DropdownMenu({
     Key key,
     this.route,
   }) : super(key: key);

packages/flutter/lib/src/material/flexible_space_bar.dart

@@ -30,7 +30,7 @@ class FlexibleSpaceBar extends StatefulWidget {
   /// Creates a flexible space bar.
   ///
   /// Most commonly used in the [AppBar.flexibleSpace] field.
-  FlexibleSpaceBar({
+  const FlexibleSpaceBar({
     Key key,
     this.title,
     this.background,
@@ -161,7 +161,7 @@ class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
 }
 
 class _FlexibleSpaceBarSettings extends InheritedWidget {
-  _FlexibleSpaceBarSettings({
+  const _FlexibleSpaceBarSettings({
     Key key,
     this.toolbarOpacity,
     this.minExtent,

packages/flutter/lib/src/material/grid_tile_bar.dart

@@ -24,7 +24,7 @@ class GridTileBar extends StatelessWidget {
   /// Creates a grid tile bar.
   ///
   /// Typically used to with [GridTile].
-  GridTileBar({
+  const GridTileBar({
     Key key,
     this.backgroundColor,
     this.leading,

packages/flutter/lib/src/material/ink_well.dart

@@ -31,7 +31,7 @@ class InkResponse extends StatefulWidget {
   /// Creates an area of a [Material] that responds to touch.
   ///
   /// Must have an ancestor [Material] widget in which to cause ink reactions.
-  InkResponse({
+  const InkResponse({
     Key key,
     this.child,
     this.onTap,
@@ -253,7 +253,7 @@ class InkWell extends InkResponse {
   /// Creates an ink well.
   ///
   /// Must have an ancestor [Material] widget in which to cause ink reactions.
-  InkWell({
+  const InkWell({
     Key key,
     Widget child,
     GestureTapCallback onTap,

packages/flutter/lib/src/material/input_decorator.dart

@@ -235,7 +235,7 @@ class InputDecoration {
 class InputDecorator extends StatelessWidget {
   /// Creates a widget that displayes labels and other visual elements similar
   /// to a [TextField].
-  InputDecorator({
+  const InputDecorator({
     Key key,
     @required this.decoration,
     this.baseStyle,

packages/flutter/lib/src/material/material.dart

@@ -358,7 +358,7 @@ class _RenderInkFeatures extends RenderProxyBox implements MaterialInkController
 }
 
 class _InkFeatures extends SingleChildRenderObjectWidget {
-  _InkFeatures({ Key key, this.color, Widget child, @required this.vsync }) : super(key: key, child: child);
+  const _InkFeatures({ Key key, this.color, Widget child, @required this.vsync }) : super(key: key, child: child);
 
   // This widget must be owned by a MaterialState, which must be provided as the vsync.
   // This relationship must be 1:1 and cannot change for the lifetime of the MaterialState.

packages/flutter/lib/src/material/mergeable_material.dart

@@ -95,7 +95,7 @@ class MaterialGap extends MergeableMaterialItem {
 ///    but otherwise looks the same.
 class MergeableMaterial extends StatefulWidget {
   /// Creates a mergeable Material list of items.
-  MergeableMaterial({
+  const MergeableMaterial({
     Key key,
     this.mainAxis: Axis.vertical,
     this.elevation: 2,
@@ -615,7 +615,7 @@ class _MergeableMaterialState extends State<MergeableMaterial> with TickerProvid
 // The parent hierarchy can change and lead to the slice being
 // rebuilt. Using a global key solves the issue.
 class _MergeableMaterialSliceKey extends GlobalKey {
-  const _MergeableMaterialSliceKey(this.value) : super.constructor();
+  _MergeableMaterialSliceKey(this.value) : super.constructor();
 
   final LocalKey value;
 

packages/flutter/lib/src/material/page.dart

@@ -3,12 +3,12 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
-import 'package:flutter/foundation.dart';  
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'theme.dart';
 
-// Fractional offset from 1/4 screen below the top to fully on screen. 
+// Fractional offset from 1/4 screen below the top to fully on screen.
 final FractionalOffsetTween _kBottomUpTween = new FractionalOffsetTween(
   begin: FractionalOffset.bottomLeft,
   end: FractionalOffset.topLeft

packages/flutter/lib/src/material/radio.dart

@@ -46,7 +46,7 @@ class Radio<T> extends StatefulWidget {
   ///
   /// * [value] and [groupValue] together determines whether the radio button is selected.
   /// * [onChanged] is when the user selects this radio button.
-  Radio({
+  const Radio({
     Key key,
     @required this.value,
     @required this.groupValue,

packages/flutter/lib/src/material/raised_button.dart

@@ -36,7 +36,7 @@ class RaisedButton extends StatelessWidget {
   ///
   /// The [child] argument is required and is typically a [Text] widget in all
   /// caps.
-  RaisedButton({
+  const RaisedButton({
     Key key,
     @required this.onPressed,
     this.color,

packages/flutter/lib/src/material/scaffold.dart

@@ -141,7 +141,7 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
 }
 
 class _FloatingActionButtonTransition extends StatefulWidget {
-  _FloatingActionButtonTransition({
+  const _FloatingActionButtonTransition({
     Key key,
     this.child,
   }) : super(key: key);
@@ -938,7 +938,7 @@ class ScaffoldFeatureController<T extends Widget, U> {
 }
 
 class _PersistentBottomSheet extends StatefulWidget {
-  _PersistentBottomSheet({
+  const _PersistentBottomSheet({
     Key key,
     this.animationController,
     this.onClosing,

packages/flutter/lib/src/material/scrollbar.dart

@@ -27,7 +27,7 @@ class Scrollbar extends StatefulWidget {
   ///
   /// The [child] should be a source of [ScrollNotification] notifications,
   /// typically a [Scrollable] widget.
-  Scrollbar({
+  const Scrollbar({
     Key key,
     @required this.child,
   }) : super(key: key);

packages/flutter/lib/src/material/slider.dart

@@ -177,7 +177,7 @@ class _SliderState extends State<Slider> with TickerProviderStateMixin {
 }
 
 class _SliderRenderObjectWidget extends LeafRenderObjectWidget {
-  _SliderRenderObjectWidget({
+  const _SliderRenderObjectWidget({
     Key key,
     this.value,
     this.divisions,

packages/flutter/lib/src/material/tab_controller.dart

@@ -170,7 +170,7 @@ class TabController extends ChangeNotifier {
 }
 
 class _TabControllerScope extends InheritedWidget {
-  _TabControllerScope({
+  const _TabControllerScope({
     Key key,
     this.controller,
     this.enabled,
@@ -227,7 +227,7 @@ class DefaultTabController extends StatefulWidget {
   /// The [length] argument must be great than one.
   ///
   /// The [initialIndex] argument must not be null.
-  DefaultTabController({
+  const DefaultTabController({
     Key key,
     @required this.length,
     this.initialIndex: 0,

packages/flutter/lib/src/material/tabs.dart

@@ -103,7 +103,7 @@ class Tab extends StatelessWidget {
 }
 
 class _TabStyle extends AnimatedWidget {
-  _TabStyle({
+  const _TabStyle({
     Key key,
     Animation<double> animation,
     this.selected,
@@ -946,7 +946,7 @@ class TabPageSelectorIndicator extends StatelessWidget {
 /// ancestor.
 class TabPageSelector extends StatelessWidget {
   /// Creates a compact widget that indicates which tab has been selected.
-  TabPageSelector({ Key key, this.controller }) : super(key: key);
+  const TabPageSelector({ Key key, this.controller }) : super(key: key);
 
   /// This widget's selection and animation state.
   ///

packages/flutter/lib/src/material/text_field.dart

@@ -62,7 +62,7 @@ class TextField extends StatefulWidget {
   /// To remove the decoration entirely (including the extra padding introduced
   /// by the decoration to save space for the labels), set the [decoration] to
   /// null.
-  TextField({
+  const TextField({
     Key key,
     this.controller,
     this.focusNode,

packages/flutter/lib/src/material/text_selection.dart

@@ -17,7 +17,7 @@ const double _kToolbarScreenPadding = 8.0; // pixels
 
 /// Manages a copy/paste text selection toolbar.
 class _TextSelectionToolbar extends StatelessWidget {
-  _TextSelectionToolbar(this.delegate, {Key key}) : super(key: key);
+  const _TextSelectionToolbar(this.delegate, {Key key}) : super(key: key);
 
   final TextSelectionDelegate delegate;
   TextEditingValue get value => delegate.textEditingValue;

packages/flutter/lib/src/material/tooltip.dart

@@ -235,7 +235,7 @@ class _TooltipPositionDelegate extends SingleChildLayoutDelegate {
 }
 
 class _TooltipOverlay extends StatelessWidget {
-  _TooltipOverlay({
+  const _TooltipOverlay({
     Key key,
     this.message,
     this.height,

packages/flutter/lib/src/material/two_level_list.dart

@@ -104,7 +104,7 @@ class TwoLevelListItem extends StatelessWidget {
 ///  * [ListTile]
 class TwoLevelSublist extends StatefulWidget {
   /// Creates an item in a two-level list that can expland and collapse.
-  TwoLevelSublist({
+  const TwoLevelSublist({
     Key key,
     this.leading,
     @required this.title,

packages/flutter/lib/src/painting/flutter_logo.dart

@@ -50,7 +50,7 @@ class FlutterLogoDecoration extends Decoration {
        // (see https://github.com/dart-lang/sdk/issues/26980 for details about that ignore statement)
        _opacity = 1.0;
 
-  FlutterLogoDecoration._(this.lightColor, this.darkColor, this.textColor, this.style, this._position, this._opacity, this.margin);
+  const FlutterLogoDecoration._(this.lightColor, this.darkColor, this.textColor, this.style, this._position, this._opacity, this.margin);
 
   /// The lighter of the two colors used to paint the logo.
   ///

packages/flutter/lib/src/rendering/box.dart

@@ -532,7 +532,7 @@ enum _IntrinsicDimension { minWidth, maxWidth, minHeight, maxHeight }
 
 @immutable
 class _IntrinsicDimensionsCacheEntry {
-  _IntrinsicDimensionsCacheEntry(this.dimension, this.argument);
+  const _IntrinsicDimensionsCacheEntry(this.dimension, this.argument);
 
   final _IntrinsicDimension dimension;
   final double argument;

packages/flutter/lib/src/rendering/sliver_grid.dart

@@ -145,7 +145,7 @@ class SliverGridRegularTileLayout extends SliverGridLayout {
   ///
   /// All of the arguments must not be null and must not be negative. The
   /// `crossAxisCount` argument must be greater than zero.
-  SliverGridRegularTileLayout({
+  const SliverGridRegularTileLayout({
     @required this.crossAxisCount,
     @required this.mainAxisStride,
     @required this.crossAxisStride,

packages/flutter/lib/src/widgets/animated_size.dart

@@ -15,7 +15,7 @@ class AnimatedSize extends SingleChildRenderObjectWidget {
   /// Creates a widget that animates its size to match that of its child.
   ///
   /// The [curve] and [duration] arguments must not be null.
-  AnimatedSize({
+  const AnimatedSize({
     Key key,
     Widget child,
     this.alignment: FractionalOffset.center,

packages/flutter/lib/src/widgets/app.dart

@@ -223,7 +223,7 @@ class _WidgetsAppState extends State<WidgetsApp> implements WidgetsBindingObserv
       performanceOverlay = new PerformanceOverlay.allEnabled(
                   checkerboardRasterCacheImages: widget.checkerboardRasterCacheImages);
     } else if (widget.checkerboardRasterCacheImages) {
-      performanceOverlay = new PerformanceOverlay(checkerboardRasterCacheImages: true);
+      performanceOverlay = const PerformanceOverlay(checkerboardRasterCacheImages: true);
     }
 
     if (performanceOverlay != null) {

packages/flutter/lib/src/widgets/async.dart

@@ -43,7 +43,7 @@ import 'package:meta/meta.dart' show required;
 ///  recent interaction is needed for widget building.
 abstract class StreamBuilderBase<T, S> extends StatefulWidget {
   /// Creates a [StreamBuilderBase] connected to the specified [stream].
-  StreamBuilderBase({ Key key, this.stream }) : super(key: key);
+  const StreamBuilderBase({ Key key, this.stream }) : super(key: key);
 
   /// The asynchronous computation to which this builder is currently connected,
   /// possibly null. When changed, the current summary is updated using

packages/flutter/lib/src/widgets/basic.dart

@@ -1787,7 +1787,7 @@ class Positioned extends ParentDataWidget<Stack> {
 
   /// Creates a Positioned object with [left], [top], [right], and [bottom] set
   /// to 0.0 unless a value for them is passed.
-  Positioned.fill({
+  const Positioned.fill({
     Key key,
     this.left: 0.0,
     this.top: 0.0,

packages/flutter/lib/src/widgets/drag_target.dart

@@ -83,7 +83,7 @@ class Draggable<T> extends StatefulWidget {
   ///
   /// The [child] and [feedback] arguments must not be null. If
   /// [maxSimultaneousDrags] is non-null, it must be non-negative.
-  Draggable({
+  const Draggable({
     Key key,
     @required this.child,
     @required this.feedback,
@@ -95,11 +95,11 @@ class Draggable<T> extends StatefulWidget {
     this.maxSimultaneousDrags,
     this.onDragStarted,
     this.onDraggableCanceled
-  }) : super(key: key) {
-    assert(child != null);
-    assert(feedback != null);
-    assert(maxSimultaneousDrags == null || maxSimultaneousDrags >= 0);
-  }
+  }) : assert(child != null),
+       assert(feedback != null),
+       assert(maxSimultaneousDrags == null || maxSimultaneousDrags >= 0),
+       super(key: key);
+
 
   /// The data that will be dropped by this draggable.
   final T data;
@@ -207,7 +207,7 @@ class LongPressDraggable<T> extends Draggable<T> {
   ///
   /// The [child] and [feedback] arguments must not be null. If
   /// [maxSimultaneousDrags] is non-null, it must be non-negative.
-  LongPressDraggable({
+  const LongPressDraggable({
     Key key,
     @required Widget child,
     @required Widget feedback,

packages/flutter/lib/src/widgets/editable_text.dart

@@ -487,7 +487,7 @@ class EditableTextState extends State<EditableText> implements TextInputClient {
 }
 
 class _Editable extends LeafRenderObjectWidget {
-  _Editable({
+  const _Editable({
     Key key,
     this.value,
     this.style,

packages/flutter/lib/src/widgets/form.dart

@@ -132,7 +132,7 @@ class FormState extends State<Form> {
 }
 
 class _FormScope extends InheritedWidget {
-  _FormScope({
+  const _FormScope({
     Key key,
     Widget child,
     FormState formState,

packages/flutter/lib/src/widgets/gesture_detector.dart

@@ -475,7 +475,7 @@ class RawGestureDetectorState extends State<RawGestureDetector> {
 }
 
 class _GestureSemantics extends SingleChildRenderObjectWidget {
-  _GestureSemantics({
+  const _GestureSemantics({
     Key key,
     Widget child,
     this.owner

packages/flutter/lib/src/widgets/grid_paper.dart

@@ -52,7 +52,7 @@ class _GridPaperPainter extends CustomPainter {
 /// Useful with a [Stack] for visualizing your layout along a grid.
 class GridPaper extends StatelessWidget {
   /// Creates a widget that draws a rectilinear grid of 1px wide lines.
-  GridPaper({
+  const GridPaper({
     Key key,
     this.color: const Color(0x7FC3E8F3),
     this.interval: 100.0,

packages/flutter/lib/src/widgets/modal_barrier.dart

@@ -12,7 +12,7 @@ import 'transitions.dart';
 /// A widget that prevents the user from interacting with widgets behind itself.
 class ModalBarrier extends StatelessWidget {
   /// Creates a widget that blocks user interaction.
-  ModalBarrier({
+  const ModalBarrier({
     Key key,
     this.color,
     this.dismissible: true
@@ -50,7 +50,7 @@ class ModalBarrier extends StatelessWidget {
 /// A widget that prevents the user from interacting with widgets behind itself.
 class AnimatedModalBarrier extends AnimatedWidget {
   /// Creates a widget that blocks user interaction.
-  AnimatedModalBarrier({
+  const AnimatedModalBarrier({
     Key key,
     Animation<Color> color,
     this.dismissible: true

packages/flutter/lib/src/widgets/notification_listener.dart

@@ -86,7 +86,7 @@ abstract class Notification {
 /// To dispatch notifications, use the [Notification.dispatch] method.
 class NotificationListener<T extends Notification> extends StatelessWidget {
   /// Creates a widget that listens for notifications.
-  NotificationListener({
+  const NotificationListener({
     Key key,
     @required this.child,
     this.onNotification

packages/flutter/lib/src/widgets/performance_overlay.dart

@@ -27,7 +27,7 @@ class PerformanceOverlay extends LeafRenderObjectWidget {
   /// Create a performance overlay that only displays specific statistics. The
   /// mask is created by shifting 1 by the index of the specific
   /// [StatisticOption] to enable.
-  PerformanceOverlay({
+  const PerformanceOverlay({
     Key key,
     this.optionsMask: 0,
     this.rasterizerThreshold: 0,

packages/flutter/lib/src/widgets/placeholder.dart

@@ -8,7 +8,7 @@ import 'framework.dart';
 /// A widget whose child can be mutated.
 class Placeholder extends StatefulWidget {
   /// Creates a widget whose child can be mutated.
-  Placeholder({ Key key }) : super(key: key);
+  const Placeholder({ Key key }) : super(key: key);
 
   @override
   PlaceholderState createState() => new PlaceholderState();

packages/flutter/lib/src/widgets/routes.dart

@@ -416,7 +416,7 @@ enum RoutePopDisposition {
 typedef Future<bool> WillPopCallback();
 
 class _ModalScope extends StatefulWidget {
-  _ModalScope({
+  const _ModalScope({
     Key key,
     this.route,
     @required this.page,

packages/flutter/lib/src/widgets/size_changed_layout_notifier.dart

@@ -39,7 +39,7 @@ class SizeChangedLayoutNotification extends LayoutChangedNotification { }
 class SizeChangedLayoutNotifier extends SingleChildRenderObjectWidget {
   /// Creates a [SizeChangedLayoutNotifier] that dispatches layout changed
   /// notifications when [child] changes layout size.
-  SizeChangedLayoutNotifier({
+  const SizeChangedLayoutNotifier({
     Key key,
     Widget child
   }) : super(key: key, child: child);

packages/flutter/lib/src/widgets/sliver.dart

@@ -230,12 +230,11 @@ class SliverChildListDelegate extends SliverChildDelegate {
 /// Helps subclasses build their children lazily using a [SliverChildDelegate].
 abstract class SliverMultiBoxAdaptorWidget extends RenderObjectWidget {
   /// Initializes fields for subclasses.
-  SliverMultiBoxAdaptorWidget({
+  const SliverMultiBoxAdaptorWidget({
     Key key,
     @required this.delegate,
-  }) : super(key: key) {
-    assert(delegate != null);
-  }
+  }) : assert(delegate != null),
+       super(key: key);
 
   /// The delegate that provides the children for this widget.
   ///
@@ -308,7 +307,7 @@ abstract class SliverMultiBoxAdaptorWidget extends RenderObjectWidget {
 ///  * [SliverGrid], which places its children in arbitrary positions.
 class SliverList extends SliverMultiBoxAdaptorWidget {
   /// Creates a sliver that places box children in a linear array.
-  SliverList({
+  const SliverList({
     Key key,
     @required SliverChildDelegate delegate,
   }) : super(key: key, delegate: delegate);
@@ -341,7 +340,7 @@ class SliverList extends SliverMultiBoxAdaptorWidget {
 class SliverFixedExtentList extends SliverMultiBoxAdaptorWidget {
   /// Creates a sliver that places box children with the same main axis extent
   /// in a linear array.
-  SliverFixedExtentList({
+  const SliverFixedExtentList({
     Key key,
     @required SliverChildDelegate delegate,
     @required this.itemExtent,
@@ -376,7 +375,7 @@ class SliverFixedExtentList extends SliverMultiBoxAdaptorWidget {
 class SliverGrid extends SliverMultiBoxAdaptorWidget {
   /// Creates a sliver that places multiple box children in a two dimensional
   /// arrangement.
-  SliverGrid({
+  const SliverGrid({
     Key key,
     @required SliverChildDelegate delegate,
     @required this.gridDelegate,
@@ -694,7 +693,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
 ///  * [SliverList], which shows a list of variable-sized children in a
 ///    viewport.
 class SliverFillRemaining extends SingleChildRenderObjectWidget {
-  SliverFillRemaining({
+  const SliverFillRemaining({
     Key key,
     Widget child,
   }) : super(key: key, child: child);

packages/flutter/lib/src/widgets/sliver_persistent_header.dart

@@ -146,12 +146,11 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
 }
 
 abstract class _SliverPersistentHeaderRenderObjectWidget extends RenderObjectWidget {
-  _SliverPersistentHeaderRenderObjectWidget({
+  const _SliverPersistentHeaderRenderObjectWidget({
     Key key,
     @required this.delegate,
-  }) : super(key: key) {
-    assert(delegate != null);
-  }
+  }) : assert(delegate != null),
+       super(key: key);
 
   final SliverPersistentHeaderDelegate delegate;
 
@@ -190,7 +189,7 @@ abstract class _RenderSliverPersistentHeaderForWidgetsMixin implements RenderSli
 }
 
 class _SliverScrollingPersistentHeader extends _SliverPersistentHeaderRenderObjectWidget {
-  _SliverScrollingPersistentHeader({
+  const _SliverScrollingPersistentHeader({
     Key key,
     @required SliverPersistentHeaderDelegate delegate,
   }) : super(key: key, delegate: delegate);
@@ -208,7 +207,7 @@ class _RenderSliverScrollingPersistentHeaderForWidgets extends _RenderSliverScro
   with _RenderSliverPersistentHeaderForWidgetsMixin { }
 
 class _SliverPinnedPersistentHeader extends _SliverPersistentHeaderRenderObjectWidget {
-  _SliverPinnedPersistentHeader({
+  const _SliverPinnedPersistentHeader({
     Key key,
     @required SliverPersistentHeaderDelegate delegate,
   }) : super(key: key, delegate: delegate);
@@ -225,7 +224,7 @@ abstract class _RenderSliverPinnedPersistentHeader extends RenderSliverPinnedPer
 class _RenderSliverPinnedPersistentHeaderForWidgets extends _RenderSliverPinnedPersistentHeader with _RenderSliverPersistentHeaderForWidgetsMixin { }
 
 class _SliverFloatingPersistentHeader extends _SliverPersistentHeaderRenderObjectWidget {
-  _SliverFloatingPersistentHeader({
+  const _SliverFloatingPersistentHeader({
     Key key,
     @required SliverPersistentHeaderDelegate delegate,
   }) : super(key: key, delegate: delegate);
@@ -250,7 +249,7 @@ abstract class _RenderSliverFloatingPinnedPersistentHeader extends RenderSliverF
 class _RenderSliverFloatingPinnedPersistentHeaderForWidgets extends _RenderSliverFloatingPinnedPersistentHeader with _RenderSliverPersistentHeaderForWidgetsMixin { }
 
 class _SliverFloatingPinnedPersistentHeader extends _SliverPersistentHeaderRenderObjectWidget {
-  _SliverFloatingPinnedPersistentHeader({
+  const _SliverFloatingPinnedPersistentHeader({
     Key key,
     @required SliverPersistentHeaderDelegate delegate,
   }) : super(key: key, delegate: delegate);

packages/flutter/lib/src/widgets/status_transitions.dart

@@ -12,12 +12,11 @@ abstract class StatusTransitionWidget extends StatefulWidget {
   /// Initializes fields for subclasses.
   ///
   /// The [animation] argument must not be null.
-  StatusTransitionWidget({
+  const StatusTransitionWidget({
     Key key,
     @required this.animation
-  }) : super(key: key) {
-    assert(animation != null);
-  }
+  }) : assert(animation != null),
+       super(key: key);
 
   /// The animation to which this widget is listening.
   final Animation<double> animation;

packages/flutter/lib/src/widgets/table.dart

@@ -355,7 +355,7 @@ class _TableElement extends RenderObjectElement {
 /// other kinds of widgets, like [RenderObjectWidget]s).
 class TableCell extends ParentDataWidget<Table> {
   /// Creates a widget that controls how a child of a [Table] is aligned.
-  TableCell({
+  const TableCell({
     Key key,
     this.verticalAlignment,
     @required Widget child

packages/flutter/lib/src/widgets/text_selection.dart

@@ -296,7 +296,7 @@ class TextSelectionOverlay implements TextSelectionDelegate {
 
 /// This widget represents a single draggable text selection handle.
 class _TextSelectionHandleOverlay extends StatefulWidget {
-  _TextSelectionHandleOverlay({
+  const _TextSelectionHandleOverlay({
     Key key,
     this.selection,
     this.position,