The dirty bits set the stage for performance improvements in D3D, but
don't actually reduce any of the redundant work just yet.

BUG=angleproject:1260

Change-Id: Ib84e6a9b7aa40c37c41790f492361b22faaf4742
Reviewed-on: https://chromium-review.googlesource.com/318730Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>