Run video.rAF callbacks in rendering steps

Currently, video.requestAnimationFrame() callbacks execute as soon as
possible on the main thread, disregarding the normal event loop
processing model.

This CL delays the execution of the video.rAF callbacks to the next time
the rendering steps are run (e.g. right before the regular window.rAF
callbacks). This makes video.rAF callback more consistent with what
web authors would expect for a method of that name.

Spec: https://wicg.github.io/video-raf/
Intent-to-prototype: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/LGPUCOCVQxs/IKVPne8wDQAJ

Bug: 1012063
Change-Id: If16dc9b76df6c732ebdfa1d1582ea34278ee0d0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040742
Commit-Queue: Thomas Guilbert <[email protected]>
Reviewed-by: Mounir Lamouri <[email protected]>
Reviewed-by: Kent Tamura <[email protected]>
Reviewed-by: Guido Urdaneta <[email protected]>
Reviewed-by: Mason Freed <[email protected]>
Reviewed-by: Dale Curtis <[email protected]>
Cr-Commit-Position: refs/heads/master@{#743016}
11 files changed