Implement window.requestPostAnimationFrame

This can only be called from within a requestAnimationFrame callback.
It registers a callback that will run synchronously at the end of a
lifecycle update, with no possibility of any other javascript running
before it.

Bug: 956293
Change-Id: I9e42ef043588134ed9ded638e1f8474eedbf800b
Reviewed-by: Klaus Weidner <>
Reviewed-by: Emil A Eklund <>
Reviewed-by: Yuki Shiino <>
Commit-Queue: Stefan Zager <>
Cr-Commit-Position: refs/heads/master@{#654321}
19 files changed