fix memory leak of android view (#50111)

packages/flutter/lib/src/services/platform_views.dart

@@ -532,6 +532,7 @@ class AndroidViewController {
       await SystemChannels.platform_views.invokeMethod<void>('dispose', id);
     _platformViewCreatedCallbacks.clear();
     _state = _AndroidViewState.disposed;
+    PlatformViewsService._instance._focusCallbacks.remove(id);
   }
 
   /// Sizes the Android View.

packages/flutter/test/services/platform_views_test.dart

@@ -85,6 +85,23 @@ void main() {
       await viewController.dispose();
     });
 
+    test('dispose clears focusCallbacks', () async {
+      bool didFocus = false;
+      viewsController.registerViewType('webview');
+      final AndroidViewController viewController = PlatformViewsService.initAndroidView(
+          id: 0,
+          viewType: 'webview',
+          layoutDirection: TextDirection.ltr,
+          onFocus: () { didFocus = true; }
+      );
+      await viewController.setSize(const Size(100.0, 100.0));
+      await viewController.dispose();
+      final ByteData message =
+          SystemChannels.platform_views.codec.encodeMethodCall(const MethodCall('viewFocused', 0));
+      await SystemChannels.platform_views.binaryMessenger.handlePlatformMessage(SystemChannels.platform_views.name, message, (_) { });
+      expect(didFocus, isFalse);
+    });
+
     test('resize Android view', () async {
       viewsController.registerViewType('webview');
       await PlatformViewsService.initAndroidView(