Don't blink in views that haven't transitioned yet.

Bug 16959262

Views that hadn't animated in during the enter transition were
being stripped from the exit transition. This caused them to
blink in as the enter transition was canceled.

This pauses the entering transition so that the view positions
are properly captured for the exit transition and aren't stripped.

Change-Id: I39cc94ed3bf92a51f8c5fe741f0aa5456b704bf0