Remove ViewTreeObserver allocations

This change replaces CopyOnWriteArrayList with a custom CopyOnWriteArray.
The new CopyOnWriteArray only allocates when a concurrent modification
is detected. Only one loop can iterate over CopyOnWriteArray at any
given time and the class is not thread safe.

Change-Id: Ie67a1ec20ff095350bf3c5d4f87cdb231ad57221