This can be used to mask out inappropriate local dirty bits.

Bug: angleproject:2763
Change-Id: Ie46e464df0dc719c963ff9f7066d42eb5a028262
Reviewed-on: https://chromium-review.googlesource.com/c/1264062
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@google.com>