Wait before asserts activity's removal

The finishing activity may not always be removed right after the top
activity resumed.

Bug: 309505574
Bug: 306375648
Test: atest ActivityStarterTests
Change-Id: Idf9efeadbef6b75eed48aa75fd6c9d5496db3c00
Merged-In: Idf9efeadbef6b75eed48aa75fd6c9d5496db3c00

Author: Louis Chang

tests/framework/base/windowmanager/src/android/server/wm/lifecycle/ActivityStarterTests.java

@@ -684,9 +684,8 @@ public void testActivityWithFinishOnTaskLaunch() {
                 .execute();
         mWmState.waitForActivityState(STANDARD_ACTIVITY, STATE_RESUMED);
 
-        // Make sure the activity is finished.
-        assertEquals("Instance of the activity in its task must be cleared", 0,
-                mWmState.getActivityCountInTask(taskId, FINISH_ON_TASK_LAUNCH_ACTIVITY));
+        // Make sure the activity is removed.
+        mWmState.waitAndAssertActivityRemoved(FINISH_ON_TASK_LAUNCH_ACTIVITY);
     }
 
     @Test