Notify task about display change when moved to new stack

Bug: 34176283
Test: android.server.cts.ActivityManagerDisplayTests
Test: #testMoveTaskBetweenDisplays
Test: bit FrameworksServicesTests:com.android.server.wm.TaskWindowContainerControllerTests
Test: bit FrameworksServicesTests:com.android.server.wm.TaskStackContainersTests
Change-Id: If085246926790089e014a94093d788805e812489
diff --git a/services/tests/servicestests/src/com/android/server/wm/WindowTestsBase.java b/services/tests/servicestests/src/com/android/server/wm/WindowTestsBase.java
index 44d5055..5a5b317 100644
--- a/services/tests/servicestests/src/com/android/server/wm/WindowTestsBase.java
+++ b/services/tests/servicestests/src/com/android/server/wm/WindowTestsBase.java
@@ -210,6 +210,7 @@
     class TestTask extends Task {
 
         boolean mShouldDeferRemoval = false;
+        boolean mOnDisplayChangedCalled = false;
 
         TestTask(int taskId, TaskStack stack, int userId, WindowManagerService service, Rect bounds,
                 Configuration overrideConfig, boolean isOnTopLauncher, int resizeMode,
@@ -225,6 +226,12 @@
         int positionInParent() {
             return getParent().mChildren.indexOf(this);
         }
+
+        @Override
+        void onDisplayChanged(DisplayContent dc) {
+            super.onDisplayChanged(dc);
+            mOnDisplayChangedCalled = true;
+        }
     }
 
     /**