This allows to validate fragment shader outputs for
shader version #300 and newer.

Change-Id: I21b21ebb357eab61e36c080c328291ed20b8eb8f
Reviewed-on: https://chromium-review.googlesource.com/497749Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>