Fix bug where app icon is gone for first frame on cold start.

We need the icon to be full alpha during the init pass, then when
the actual animation starts, we can swap the icon with the window
(splash screen that draws the icon).

Bug: 192366079
Test: slow down window animations
      check no empty frame on cold start app launch
      check no empty frame on warm start app launch

Change-Id: I16a1779e5252d8e88bc3c408e1dc40b264fe4cf4