MIgrate ios_platform_view_tests to null safety (#80619)

dev/integration_tests/ios_platform_view_tests/lib/main.dart

@@ -12,7 +12,7 @@ void main() {
 
 /// The main app entrance of the test
 class MyApp extends StatelessWidget {
-  const MyApp({Key key}) : super(key: key);
+  const MyApp({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -30,8 +30,8 @@ class MyApp extends StatelessWidget {
 ///
 /// On press the button, a page with platform view should be pushed into the scene.
 class MyHomePage extends StatefulWidget {
-  const MyHomePage({Key key, this.title}) : super(key: key);
-  final String title;
+  const MyHomePage({Key? key, this.title}) : super(key: key);
+  final String? title;
 
   @override
   _MyHomePageState createState() => _MyHomePageState();
@@ -42,7 +42,7 @@ class _MyHomePageState extends State<MyHomePage> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text(widget.title),
+        title: Text(widget.title ?? ''),
       ),
       body: Column(children: <Widget>[
         TextButton(
@@ -69,7 +69,7 @@ class _MyHomePageState extends State<MyHomePage> {
 
 /// A page contains the platform view to be tested.
 class PlatformViewPage extends StatelessWidget {
-  const PlatformViewPage({Key key}) : super(key: key);
+  const PlatformViewPage({Key? key}) : super(key: key);
 
   static Key button = const ValueKey<String>('plus_button');
 

dev/integration_tests/ios_platform_view_tests/pubspec.yaml

@@ -3,7 +3,7 @@ name: ios_platform_view_tests
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:

dev/integration_tests/ios_platform_view_tests/test_driver/main_test.dart

@@ -8,7 +8,7 @@ import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
 
 void main() {
   group('FlutterDriver', () {
-    FlutterDriver driver;
+    late FlutterDriver driver;
 
     setUpAll(() async {
       driver = await FlutterDriver.connect();