This is not a complete implementation because it does not have the
ability to disable the physical device feature. It does pass the
current set of robust access tests. But there could be a performance
regression on platforms that have a slower impelmentation. We would
want the ability to support cases with bufer robustness on or off.

Bug: angleproject:3062
Change-Id: I7d6eb889debcbd32f6ed809b526677123f872726
Reviewed-on: https://chromium-review.googlesource.com/c/1403967Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>