Fix flicker with remote animations

There was a race condition where we notified the controlling app
already about transition start, which itself started the animation
and applied the transform of the first frame. However, a little
bit later, we applied the pending transaction from window manager,
which overrode the properties again, leading to a flicker.

Test: go/wm-smoke
Test: Press home button, observe never a flicker
Bug: Surprisingly there isn't one yet.
Change-Id: I849a1573e6fd0487b9b5c22c7a7525bc818661cc