Add chrome://flags entry to select overlay strategies

This patch adds a multi-value entry in about://flags that will
help enabling/disabling HW overlay strategies used to promote quads
to HW overlays.

Bug: 854677
Change-Id: Ibaedb02084a0b6aea490637bd6c4456caa63e29d
Reviewed-on: https://chromium-review.googlesource.com/1108520
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569403}
4 files changed