Fix leak fix in ViewTreeObserver

The leak fix of the CopyOnWriteArray in ViewTreeObserver was
too aggressive, always clearing the shadow copy when it should only
have cleared it when needed. The way it works now, we will always
clear the listeners for ViewTreeObserver after the listeners
are processed.

Issue #10815924 ViewTreeObserver leak fix too aggressive

Change-Id: Iff0095d73beb38e52b0a5ae6b6378afec4458fd3