Pushing the startActivity before the calls to remove task.

- It appears that there is contention between startActivityAsUser() and
  removeTask() (called on two separate threads) which can cause jank when
  a user removes all the tasks from their recents list.  This CL ensures
  that startActivityAsUser() is always run first so it is not blocked
  by the other call (which should be able to run in the background
  uninterrupted).

Bug: 22760556
Change-Id: I7564a2f0e43414686419d3657379bbd0ca6b4152

packages/SystemUI/src/com/android/systemui/recents/views/TaskStackView.java

@@ -1121,9 +1121,6 @@ public class TaskStackView extends FrameLayout implements TaskStack.TaskStackCal
             mViewPool.returnViewToPool(tv);
         }
 
-        // Notify the callback that we've removed the task and it can clean up after it
-        mCb.onTaskViewDismissed(removedTask);
-
         // Get the stack scroll of the task to anchor to (since we are removing something, the front
         // most task will be our anchor task)
         Task anchorTask = null;
@@ -1172,6 +1169,11 @@ public class TaskStackView extends FrameLayout implements TaskStack.TaskStackCal
             // Fade the dismiss button back in
             showDismissAllButton();
         }
+
+        // Notify the callback that we've removed the task and it can clean up after it. Note, we
+        // do this after onAllTaskViewsDismissed() is called, to allow the home activity to be
+        // started before the call to remove the task.
+        mCb.onTaskViewDismissed(removedTask);
     }
 
     @Override