Put the view focus functionality behind a (disabled by default) flag (#52527)

Put the view focus functionality behind a (disabled by default) flag

Should unblock flutter/flutter#143259

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: tugorez

lib/web_ui/lib/src/engine/platform_dispatcher/view_focus_binding.dart

@@ -3,13 +3,21 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'package:meta/meta.dart';
 import 'package:ui/src/engine.dart';
 import 'package:ui/ui.dart' as ui;
 
 /// Tracks the [FlutterView]s focus changes.
 final class ViewFocusBinding {
   ViewFocusBinding(this._viewManager, this._onViewFocusChange);
 
+
+  /// Wether [FlutterView] focus changes will be reported and performed.
+  ///
+  /// DO NOT rely on this bit as it will go away soon. You're warned :)!
+  @visibleForTesting
+  static bool isEnabled = false;
+
   final FlutterViewManager _viewManager;
   final ui.ViewFocusChangeCallback _onViewFocusChange;
 
@@ -35,6 +43,9 @@ final class ViewFocusBinding {
   }
 
   void changeViewFocus(int viewId, ui.ViewFocusState state) {
+    if (!isEnabled) {
+      return;
+    }
     final DomElement? viewElement = _viewManager[viewId]?.dom.rootElement;
 
     if (state == ui.ViewFocusState.focused) {
@@ -69,6 +80,10 @@ final class ViewFocusBinding {
   });
 
   void _handleFocusChange(DomElement? focusedElement) {
+    if (!isEnabled) {
+      return;
+    }
+
     final int? viewId = _viewId(focusedElement);
     if (viewId == _lastViewId) {
       return;

lib/web_ui/test/engine/platform_dispatcher/view_focus_binding_test.dart

@@ -17,14 +17,18 @@ void testMain() {
     late EnginePlatformDispatcher dispatcher;
 
     setUp(() {
-      domDocument.activeElement?.blur();
-      EngineSemantics.instance.semanticsEnabled = false;
+      ViewFocusBinding.isEnabled = true;
 
       dispatcher = EnginePlatformDispatcher.instance;
       dispatchedViewFocusEvents = <ui.ViewFocusEvent>[];
       dispatcher.onViewFocusChange = dispatchedViewFocusEvents.add;
     });
 
+    tearDown(() {
+      ViewFocusBinding.isEnabled = false;
+      EngineSemantics.instance.semanticsEnabled = false;
+    });
+
     test('The view is focusable and reachable by keyboard when registered', () async {
       final EngineFlutterView view = createAndRegisterView(dispatcher);