This will make it easier to do state update on context switch.

BUG=angleproject:2052

Change-Id: Ia73cfd07ced40a9e22d6b34a5619250ede9e8844
Reviewed-on: https://chromium-review.googlesource.com/659233Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>