Fix flaky TaskStackChangedListenerTest

The test was flaky is because the activity can be killed before the test
finished running.

The test activity would be killed in onPostResumed and the latch count
down is happening in onResumed. After that, the test was trying to
access task ID via the activity. It is possible that when accessing
task ID, the activity is no longer there.

To fix that, keep the task ID when creating the activity in the test.
This will significantly reduce, if not eliminate, the flakiness inside.

Mark as pre-submit candidate to be monitored.

Test: atest TaskStackChangedListenerTest
Bug: 119893767
Change-Id: I3826282b395169097cb3496e47557d622a8fc856

services/tests/wmtests/src/com/android/server/wm/TaskStackChangedListenerTest.java

@@ -100,7 +100,7 @@ public class TaskStackChangedListenerTest {
     }
 
     @Test
-    @FlakyTest(bugId = 119893767)
+    @FlakyTest(detail = "Promote to presubmit when shown to be stable.")
     public void testTaskDescriptionChanged() throws Exception {
         final Object[] params = new Object[2];
         final CountDownLatch latch = new CountDownLatch(1);
@@ -122,14 +122,18 @@ public class TaskStackChangedListenerTest {
                 }
             }
         });
-        final Activity activity = startTestActivity(ActivityTaskDescriptionChange.class);
+
+        int taskId;
+        synchronized (sLock) {
+            taskId = startTestActivity(ActivityTaskDescriptionChange.class).getTaskId();
+        }
         waitForCallback(latch);
-        assertEquals(activity.getTaskId(), params[0]);
+        assertEquals(taskId, params[0]);
         assertEquals("Test Label", ((TaskDescription) params[1]).getLabel());
     }
 
     @Test
-    @FlakyTest(bugId = 119893767)
+    @FlakyTest(detail = "Promote to presubmit when shown to be stable.")
     public void testActivityRequestedOrientationChanged() throws Exception {
         final int[] params = new int[2];
         final CountDownLatch latch = new CountDownLatch(1);
@@ -142,9 +146,12 @@ public class TaskStackChangedListenerTest {
                 latch.countDown();
             }
         });
-        final Activity activity = startTestActivity(ActivityRequestedOrientationChange.class);
+        int taskId;
+        synchronized (sLock) {
+            taskId = startTestActivity(ActivityRequestedOrientationChange.class).getTaskId();
+        }
         waitForCallback(latch);
-        assertEquals(activity.getTaskId(), params[0]);
+        assertEquals(taskId, params[0]);
         assertEquals(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT, params[1]);
     }
 
@@ -152,7 +159,7 @@ public class TaskStackChangedListenerTest {
      * Tests for onTaskCreated, onTaskMovedToFront, onTaskRemoved and onTaskRemovalStarted.
      */
     @Test
-    @FlakyTest(bugId = 119893767)
+    @FlakyTest(detail = "Promote to presubmit when shown to be stable.")
     public void testTaskChangeCallBacks() throws Exception {
         final Object[] params = new Object[2];
         final CountDownLatch taskCreatedLaunchLatch = new CountDownLatch(1);
@@ -245,7 +252,7 @@ public class TaskStackChangedListenerTest {
 
     private void waitForCallback(CountDownLatch latch) {
         try {
-            final boolean result = latch.await(2, TimeUnit.SECONDS);
+            final boolean result = latch.await(4, TimeUnit.SECONDS);
             if (!result) {
                 throw new RuntimeException("Timed out waiting for task stack change notification");
             }
@@ -324,7 +331,11 @@ public class TaskStackChangedListenerTest {
         protected void onPostResume() {
             super.onPostResume();
             setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
-            finish();
+            synchronized (sLock) {
+                // Hold the lock to ensure no one is trying to access fields of this Activity in
+                // this test.
+                finish();
+            }
         }
     }
 
@@ -333,7 +344,11 @@ public class TaskStackChangedListenerTest {
         protected void onPostResume() {
             super.onPostResume();
             setTaskDescription(new TaskDescription("Test Label"));
-            finish();
+            synchronized (sLock) {
+                // Hold the lock to ensure no one is trying to access fields of this Activity in
+                // this test.
+                finish();
+            }
         }
     }