Fix the flickering on display/font size page

In framework design, framework needs to have a snapshot
when there's a config change event since redrawing window
takes some time.
Flickering problem is caused by the timing issue between the
snapshot mechinsm and local preview update.

User can observe the flickering problem if config commit()->
snapshot in framework(old screenshot) -> app update the preview
-> snapshot(old screen) fade out.

To prevent this problem, we make sure that we update the local preview
first and then we do the commit later. In this proposal, snapshot action
is able to get the new snaptshot for the new preview.

So, the core workaround is commitOnNextFrame, we ask a delay before
we submit the commit(). Note: It doesn't matter that we use
Choreographer or main thread handler since the delay time is longer
than 1 frame. Use Choreographer to let developer understand it's a
window update.

Fix: 148192402
Test: manual test
Change-Id: I9bfc5eb39e7a9ebce2fe1414d6f0a9dd470708e8