Fixing a memory leak in About box/dialog overlays (#130842)

## Description

Fix three memory leaks detected by `about_test.dart`, but were really in the `Route` and `OverlayEntry` classes.

## Related Issues
 - Fixes https://github.com/flutter/flutter/issues/130354

## Tests
 - Updates about_test.dart to not ignore the leaks anymore.

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

@@ -2861,11 +2861,11 @@ class _RouteEntry extends RouteTransitionRecord {
   final _RestorationInformation? restorationInformation;
   final bool pageBased;
 
-  static Route<dynamic> notAnnounced = _NotAnnounced();
+  static final Route<dynamic> notAnnounced = _NotAnnounced();
 
   _RouteLifecycle currentState;
   Route<dynamic>? lastAnnouncedPreviousRoute = notAnnounced; // last argument to Route.didChangePrevious
-  Route<dynamic> lastAnnouncedPoppedNextRoute = notAnnounced; // last argument to Route.didPopNext
+  WeakReference<Route<dynamic>> lastAnnouncedPoppedNextRoute = WeakReference<Route<dynamic>>(notAnnounced); // last argument to Route.didPopNext
   Route<dynamic>? lastAnnouncedNextRoute = notAnnounced; // last argument to Route.didChangeNext
 
   /// Restoration ID to be used for the encapsulating route when restoration is
@@ -2954,7 +2954,7 @@ class _RouteEntry extends RouteTransitionRecord {
 
   void handleDidPopNext(Route<dynamic> poppedRoute) {
     route.didPopNext(poppedRoute);
-    lastAnnouncedPoppedNextRoute = poppedRoute;
+    lastAnnouncedPoppedNextRoute = WeakReference<Route<dynamic>>(poppedRoute);
   }
 
   /// Process the to-be-popped route.
@@ -3153,7 +3153,7 @@ class _RouteEntry extends RouteTransitionRecord {
     // already announced this change by calling didPopNext.
     return !(
       nextRoute == null &&
-        lastAnnouncedPoppedNextRoute == lastAnnouncedNextRoute
+        lastAnnouncedPoppedNextRoute.target == lastAnnouncedNextRoute
     );
   }
 

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

@@ -135,20 +135,20 @@ class OverlayEntry implements Listenable {
   /// Whether the [OverlayEntry] is currently mounted in the widget tree.
   ///
   /// The [OverlayEntry] notifies its listeners when this value changes.
-  bool get mounted => _overlayEntryStateNotifier.value != null;
+  bool get mounted => _overlayEntryStateNotifier?.value != null;
 
   /// The currently mounted `_OverlayEntryWidgetState` built using this [OverlayEntry].
-  final ValueNotifier<_OverlayEntryWidgetState?> _overlayEntryStateNotifier = ValueNotifier<_OverlayEntryWidgetState?>(null);
+  ValueNotifier<_OverlayEntryWidgetState?>? _overlayEntryStateNotifier = ValueNotifier<_OverlayEntryWidgetState?>(null);
 
   @override
   void addListener(VoidCallback listener) {
     assert(!_disposedByOwner);
-    _overlayEntryStateNotifier.addListener(listener);
+    _overlayEntryStateNotifier?.addListener(listener);
   }
 
   @override
   void removeListener(VoidCallback listener) {
-    _overlayEntryStateNotifier.removeListener(listener);
+    _overlayEntryStateNotifier?.removeListener(listener);
   }
 
   OverlayState? _overlay;
@@ -194,7 +194,8 @@ class OverlayEntry implements Listenable {
   void _didUnmount() {
     assert(!mounted);
     if (_disposedByOwner) {
-      _overlayEntryStateNotifier.dispose();
+      _overlayEntryStateNotifier?.dispose();
+      _overlayEntryStateNotifier = null;
     }
   }
 
@@ -217,7 +218,11 @@ class OverlayEntry implements Listenable {
     assert(_overlay == null, 'An OverlayEntry must first be removed from the Overlay before dispose is called.');
     _disposedByOwner = true;
     if (!mounted) {
-      _overlayEntryStateNotifier.dispose();
+      // If we're still mounted when disposed, then this will be disposed in
+      // _didUnmount, to allow notifications to occur until the entry is
+      // unmounted.
+      _overlayEntryStateNotifier?.dispose();
+      _overlayEntryStateNotifier = null;
     }
   }
 
@@ -315,7 +320,7 @@ class _OverlayEntryWidgetState extends State<_OverlayEntryWidget> {
   @override
   void initState() {
     super.initState();
-    widget.entry._overlayEntryStateNotifier.value = this;
+    widget.entry._overlayEntryStateNotifier!.value = this;
     _theater = context.findAncestorRenderObjectOfType<_RenderTheater>()!;
     assert(_sortedTheaterSiblings == null);
   }
@@ -335,7 +340,7 @@ class _OverlayEntryWidgetState extends State<_OverlayEntryWidget> {
 
   @override
   void dispose() {
-    widget.entry._overlayEntryStateNotifier.value = null;
+    widget.entry._overlayEntryStateNotifier?.value = null;
     widget.entry._didUnmount();
     _sortedTheaterSiblings = null;
     super.dispose();
@@ -917,9 +922,9 @@ class _TheaterParentData extends StackParentData {
   // _overlayStateMounted is set to null in _OverlayEntryWidgetState's dispose
   // method. This property is only accessed during layout, paint and hit-test so
   // the `value!` should be safe.
-  Iterator<RenderBox>? get paintOrderIterator => overlayEntry?._overlayEntryStateNotifier.value!._paintOrderIterable.iterator;
-  Iterator<RenderBox>? get hitTestOrderIterator => overlayEntry?._overlayEntryStateNotifier.value!._hitTestOrderIterable.iterator;
-  void visitChildrenOfOverlayEntry(RenderObjectVisitor visitor) => overlayEntry?._overlayEntryStateNotifier.value!._paintOrderIterable.forEach(visitor);
+  Iterator<RenderBox>? get paintOrderIterator => overlayEntry?._overlayEntryStateNotifier?.value!._paintOrderIterable.iterator;
+  Iterator<RenderBox>? get hitTestOrderIterator => overlayEntry?._overlayEntryStateNotifier?.value!._hitTestOrderIterable.iterator;
+  void visitChildrenOfOverlayEntry(RenderObjectVisitor visitor) => overlayEntry?._overlayEntryStateNotifier?.value!._paintOrderIterable.forEach(visitor);
 }
 
 class _RenderTheater extends RenderBox with ContainerRenderObjectMixin<RenderBox, StackParentData>, _RenderTheaterMixin {

packages/flutter/test/gestures/gesture_config_regression_test.dart

@@ -11,6 +11,7 @@ import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
 class TestResult {
   bool dragStarted = false;
   bool dragUpdate = false;
+  bool dragEnd = false;
 }
 
 class NestedScrollableCase extends StatelessWidget {
@@ -77,7 +78,9 @@ class NestedDraggableCase extends StatelessWidget {
                     onDragUpdate: (DragUpdateDetails details){
                       testResult.dragUpdate = true;
                     },
-                    onDragEnd: (_) {},
+                    onDragEnd: (_) {
+                      testResult.dragEnd = true;
+                    },
                   ),
                 );
               },
@@ -134,5 +137,6 @@ void main() {
 
    expect(result.dragStarted, true);
    expect(result.dragUpdate, true);
+   expect(result.dragEnd, true);
   });
 }

packages/flutter/test/material/about_test.dart

@@ -282,15 +282,7 @@ void main() {
     await tester.tap(find.text('Another package'));
     await tester.pumpAndSettle();
     expect(find.text('Another license'), findsOneWidget);
-  },
-  leakTrackingTestConfig: const LeakTrackingTestConfig(
-    // TODO(polina-c): remove after fixing
-    // https://github.com/flutter/flutter/issues/130354
-    notGCedAllowList: <String, int?>{
-      'ValueNotifier<_OverlayEntryWidgetState?>': 2,
-      'ValueNotifier<String?>': 1,
-    },
-  ));
+  });
 
   testWidgetsWithLeakTracking('LicensePage control test with all properties', (WidgetTester tester) async {
     const FlutterLogo logo = FlutterLogo();
@@ -366,15 +358,7 @@ void main() {
     await tester.tap(find.text('Another package'));
     await tester.pumpAndSettle();
     expect(find.text('Another license'), findsOneWidget);
-  },
-  leakTrackingTestConfig: const LeakTrackingTestConfig(
-    // TODO(polina-c): remove after fixing
-    // https://github.com/flutter/flutter/issues/130354
-    notGCedAllowList: <String, int?>{
-      'ValueNotifier<_OverlayEntryWidgetState?>':2,
-      'ValueNotifier<String?>': 1,
-    },
-  ));
+  });
 
   testWidgetsWithLeakTracking('Material2 - _PackageLicensePage title style without AppBarTheme', (WidgetTester tester) async {
     LicenseRegistry.addLicense(() {