This will be useful for validation state caching.

Bug: angleproject:2747
Change-Id: I0737adca7406f79b9e15429f30ae22e1299cd7e4
Reviewed-on: https://chromium-review.googlesource.com/1158611
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>