Fix leakage of DisplayContent referenced from TransitionController

Unlike AppTransition which is associated DisplayContent, the
TransitionController is a global instance. So it needs to unregister
the listener when the display is removed.

Bug: 214991741
Test: Start/stop screen recording multiple times (create virtual
      display). The heap dump of system server should not contain
      many DisplayContent instances.
Change-Id: I44e2a794981fc114ada0ce98cd2471adf623d856

services/core/java/com/android/server/wm/DisplayContent.java

@@ -1067,8 +1067,6 @@ class DisplayContent extends RootDisplayArea implements WindowManagerPolicy.Disp
 
         mAppTransition = new AppTransition(mWmService.mContext, mWmService, this);
         mAppTransition.registerListenerLocked(mWmService.mActivityManagerAppTransitionNotifier);
-        mTransitionController.registerLegacyListener(
-                mWmService.mActivityManagerAppTransitionNotifier);
         mAppTransition.registerListenerLocked(mFixedRotationTransitionListener);
         mAppTransitionController = new AppTransitionController(mWmService, this);
         mUnknownAppVisibilityController = new UnknownAppVisibilityController(mWmService, this);

services/core/java/com/android/server/wm/DisplayPolicy.java

@@ -3311,6 +3311,7 @@ public class DisplayPolicy {
     }
 
     void release() {
+        mDisplayContent.mTransitionController.unregisterLegacyListener(mAppTransitionListener);
         mHandler.post(mGestureNavigationSettingsObserver::unregister);
     }
 

services/core/java/com/android/server/wm/TransitionController.java

@@ -430,6 +430,10 @@ class TransitionController {
         mLegacyListeners.add(listener);
     }
 
+    void unregisterLegacyListener(WindowManagerInternal.AppTransitionListener listener) {
+        mLegacyListeners.remove(listener);
+    }
+
     void dispatchLegacyAppTransitionPending() {
         for (int i = 0; i < mLegacyListeners.size(); ++i) {
             mLegacyListeners.get(i).onAppTransitionPendingLocked();

services/core/java/com/android/server/wm/WindowOrganizerController.java

@@ -137,6 +137,7 @@ class WindowOrganizerController extends IWindowOrganizerController.Stub
 
     void setWindowManager(WindowManagerService wms) {
         mTransitionController = new TransitionController(mService, wms.mTaskSnapshotController);
+        mTransitionController.registerLegacyListener(wms.mActivityManagerAppTransitionNotifier);
     }
 
     TransitionController getTransitionController() {