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