[null-safety] opt driver tests into null safety (#70245)

dev/integration_tests/flutter_gallery/test_driver/run_demos.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
 import 'dart:ui';
 
 import 'package:flutter/cupertino.dart';
@@ -26,7 +25,7 @@ final List<String> kSkippedDemos = <String>[
 /// home screen twice.
 Future<void> runDemos(List<String> demos, WidgetController controller) async {
   final Finder demoList = find.byType(Scrollable);
-  String currentDemoCategory;
+  String? currentDemoCategory;
 
   for (final String demo in demos) {
     if (kSkippedDemos.contains(demo))

dev/integration_tests/flutter_gallery/test_driver/scroll_perf.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
 import 'package:flutter_driver/driver_extension.dart';
 import 'package:flutter_gallery/gallery/app.dart' show GalleryApp;
 import 'package:flutter/material.dart';

dev/integration_tests/flutter_gallery/test_driver/transitions_perf.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
 import 'dart:convert' show JsonEncoder;
 
 import 'package:flutter_driver/driver_extension.dart';
@@ -25,20 +24,20 @@ List<String> _allDemos = kAllGalleryDemos.map(
 Set<String> _unTestedDemos = Set<String>.from(_allDemos);
 
 class _MessageHandler {
-  static LiveWidgetController controller;
+  static LiveWidgetController? controller;
   Future<String> call(String message) async {
     switch(message) {
       case 'demoNames':
         return const JsonEncoder.withIndent('  ').convert(_allDemos);
       case 'profileDemos':
-        controller ??= LiveWidgetController(WidgetsBinding.instance);
-        await runDemos(kProfiledDemos, controller);
+        controller ??= LiveWidgetController(WidgetsBinding.instance!);
+        await runDemos(kProfiledDemos, controller!);
         _unTestedDemos.removeAll(kProfiledDemos);
         return const JsonEncoder.withIndent('  ').convert(kProfiledDemos);
       case 'restDemos':
-        controller ??= LiveWidgetController(WidgetsBinding.instance);
+        controller ??= LiveWidgetController(WidgetsBinding.instance!);
         final List<String> restDemos =  _unTestedDemos.toList();
-        await runDemos(restDemos, controller);
+        await runDemos(restDemos, controller!);
         return const JsonEncoder.withIndent('  ').convert(restDemos);
       default:
         throw ArgumentError;
@@ -47,7 +46,7 @@ class _MessageHandler {
 }
 
 void main() {
-  enableFlutterDriverExtension(handler: _MessageHandler().call);
+  enableFlutterDriverExtension(handler: (String? message) => _MessageHandler().call(message!));
   // As in lib/main.dart: overriding https://github.com/flutter/flutter/issues/13736
   // for better visual effect at the cost of performance.
   runApp(const GalleryApp(testMode: true));

dev/integration_tests/flutter_gallery/test_memory/back_button.dart

@@ -4,7 +4,6 @@
 
 // See //dev/devicelab/bin/tasks/flutter_gallery__memory_nav.dart
 
-// @dart = 2.9
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_gallery/gallery/app.dart' show GalleryApp;
@@ -12,8 +11,8 @@ import 'package:flutter_test/flutter_test.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance.hasScheduledFrame);
+    await SchedulerBinding.instance!.endOfFrame;
+  } while (SchedulerBinding.instance!.hasScheduledFrame);
 }
 
 int iteration = 0;
@@ -31,5 +30,5 @@ Future<void> main() async {
   await endOfAnimation();
   await Future<void>.delayed(const Duration(milliseconds: 50));
   debugPrint('==== MEMORY BENCHMARK ==== READY ====');
-  WidgetsBinding.instance.addObserver(LifecycleObserver());
+  WidgetsBinding.instance!.addObserver(LifecycleObserver());
 }

dev/integration_tests/flutter_gallery/test_memory/image_cache_memory.dart

@@ -4,7 +4,6 @@
 
 // See //dev/devicelab/bin/tasks/flutter_gallery__image_cache_memory.dart
 
-// @dart = 2.9
 import 'package:flutter/widgets.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -39,7 +38,7 @@ Future<void> main() async {
     ),
   ));
 
-  await SchedulerBinding.instance.endOfFrame;
+  await SchedulerBinding.instance!.endOfFrame;
 
   // We are waiting for the GPU to rasterize a frame here. This makes this
   // flaky, we can rely on a more deterministic source such as
@@ -49,7 +48,7 @@ Future<void> main() async {
   debugPrint('==== MEMORY BENCHMARK ==== READY ====');
 
   final WidgetController controller =
-      LiveWidgetController(WidgetsBinding.instance);
+      LiveWidgetController(WidgetsBinding.instance!);
 
   debugPrint('Scrolling...');
   final Finder list = find.byKey(const Key('ImageList'));

dev/integration_tests/flutter_gallery/test_memory/memory_nav.dart

@@ -4,7 +4,6 @@
 
 // See //dev/devicelab/bin/tasks/flutter_gallery__memory_nav.dart
 
-// @dart = 2.9
 import 'dart:async';
 
 import 'package:flutter/material.dart';
@@ -14,8 +13,8 @@ import 'package:flutter_test/flutter_test.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance.hasScheduledFrame);
+    await SchedulerBinding.instance!.endOfFrame;
+  } while (SchedulerBinding.instance!.hasScheduledFrame);
 }
 
 Rect boundsFor(WidgetController controller, Finder item) {
@@ -36,7 +35,7 @@ Future<void> main() async {
       child: GalleryApp(testMode: true),
     ),
   ));
-  await SchedulerBinding.instance.endOfFrame;
+  await SchedulerBinding.instance!.endOfFrame;
   await Future<void>.delayed(const Duration(milliseconds: 50));
   debugPrint('==== MEMORY BENCHMARK ==== READY ====');
 
@@ -50,9 +49,9 @@ Future<void> main() async {
       child: GalleryApp(testMode: true),
     ),
   ));
-  await SchedulerBinding.instance.endOfFrame;
+  await SchedulerBinding.instance!.endOfFrame;
 
-  final WidgetController controller = LiveWidgetController(WidgetsBinding.instance);
+  final WidgetController controller = LiveWidgetController(WidgetsBinding.instance!);
 
   debugPrint('Navigating...');
   await controller.tap(find.text('Material'));