Fixing activity leak on config change

If attachTo happens before the view is attached to window,
ViewOnDrawExecutor hooks to the tree observer twice (second time from
onViewAttachedToWindow). It only unhooks once.

Since tree observer is global, this leads to leaking the activity, and
besides, all old activities getting the events from the tree observer.

Bug: 139137636
Change-Id: Ie2641b8f3614545052fe34ad6588b070c3b82a33

src/com/android/launcher3/util/ViewOnDrawExecutor.java

@@ -55,7 +55,9 @@ public class ViewOnDrawExecutor implements Executor, OnDrawListener, Runnable,
             mLoadAnimationCompleted = true;
         }
 
-        attachObserver();
+        if (mAttachedView.isAttachedToWindow()) {
+            attachObserver();
+        }
     }
 
     private void attachObserver() {