This will ensure our currently set pixel and vertex SRVs match with
the underlying D3D state, and reduce the need for resetting them as
often.

BUG=angle:756
BUG=417424

Change-Id: I42e9e25182b279871ac4cdf8da5e2ab62c8cf71f
Reviewed-on: https://chromium-review.googlesource.com/225052Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>