ScrollActivity should dispatch creation and disposal events. (#137961)

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

@@ -57,7 +57,17 @@ abstract class ScrollActivityDelegate {
 ///    [ScrollPosition] of a [Scrollable].
 abstract class ScrollActivity {
   /// Initializes [delegate] for subclasses.
-  ScrollActivity(this._delegate);
+  ScrollActivity(this._delegate) {
+    // TODO(polina-c): stop duplicating code across disposables
+    // https://github.com/flutter/flutter/issues/137435
+    if (kFlutterMemoryAllocationsEnabled) {
+      MemoryAllocations.instance.dispatchObjectCreated(
+        library: 'package:flutter/widgets.dart',
+        className: '$ScrollActivity',
+        object: this,
+      );
+    }
+  }
 
   /// The delegate that this activity will use to actuate the scroll view.
   ScrollActivityDelegate get delegate => _delegate;
@@ -137,6 +147,12 @@ abstract class ScrollActivity {
   /// Called when the scroll view stops performing this activity.
   @mustCallSuper
   void dispose() {
+    // TODO(polina-c): stop duplicating code across disposables
+    // https://github.com/flutter/flutter/issues/137435
+    if (kFlutterMemoryAllocationsEnabled) {
+      MemoryAllocations.instance.dispatchObjectDisposed(object: this);
+    }
+
     _isDisposed = true;
   }
 

packages/flutter/test/widgets/scroll_activity_test.dart

@@ -212,6 +212,16 @@ void main() {
     expect(lastTapped, equals(3));
     await tester.pumpAndSettle();
   });
+
+  test('$ScrollActivity dispatches memory events', () async {
+    await expectLater(
+      await memoryEvents(
+        () => _ScrollActivity(_ScrollActivityDelegate()).dispose(),
+        _ScrollActivity,
+      ),
+      areCreateAndDispose,
+    );
+  });
 }
 
 class PageView62209 extends StatefulWidget {
@@ -359,3 +369,33 @@ class _Carousel62209State extends State<Carousel62209> {
     );
   }
 }
+
+class _ScrollActivity extends ScrollActivity {
+  _ScrollActivity(super.delegate);
+
+  @override
+  bool get isScrolling => false;
+
+  @override
+  bool get shouldIgnorePointer => true;
+
+  @override
+  double get velocity => 0.0;
+}
+
+class _ScrollActivityDelegate extends ScrollActivityDelegate {
+  @override
+  void applyUserOffset(double delta) {}
+
+  @override
+  AxisDirection get axisDirection => AxisDirection.down;
+
+  @override
+  void goBallistic(double velocity) {}
+
+  @override
+  void goIdle() {}
+
+  @override
+  double setPixels(double pixels) => 0.0;
+}