Reset dummy stack view tasks after computing transition into Recents

- Also clear up references from the app transition spec future to the
  parent implementation, which can also leak memory.

Bug: 73961798
Test: Enter recents, ensure that dummy stack view holds no task refs
Change-Id: I0c466350c1c1dd490f8776ca23f13de0d698e060

packages/SystemUI/shared/src/com/android/systemui/shared/recents/view/AppTransitionAnimationSpecsFuture.java

@@ -49,6 +49,10 @@ public abstract class AppTransitionAnimationSpecsFuture {
                     mHandler.post(mComposeTask);
                 }
                 List<AppTransitionAnimationSpecCompat> specs = mComposeTask.get();
+                // Clear reference to the compose task this future holds onto the reference to it's
+                // implementation (which can leak references to the bitmap it creates for the
+                // transition)
+                mComposeTask = null;
                 if (specs == null) {
                     return null;
                 }

packages/SystemUI/src/com/android/systemui/recents/RecentsImpl.java

@@ -276,6 +276,9 @@ public class RecentsImpl implements ActivityOptions.OnAnimationFinishedListener
         }
     };
 
+    // Used to reset the dummy stack view
+    private final TaskStack mEmptyTaskStack = new TaskStack();
+
     public RecentsImpl(Context context) {
         mContext = context;
         mHandler = new Handler();
@@ -1108,6 +1111,10 @@ public class RecentsImpl implements ActivityOptions.OnAnimationFinishedListener
             }
         });
         EventBus.getDefault().send(hideMenuEvent);
+
+        // Once we have launched the activity, reset the dummy stack view tasks so we don't hold
+        // onto references to the same tasks consumed by the activity
+        mDummyStackView.setTasks(mEmptyTaskStack, false /* notifyStackChanges */);
     }
 
     /**** OnAnimationFinishedListener Implementation ****/