ES31: Validate fragment shader outputs This allows to validate fragment shader outputs for shader version #300 and newer. Change-Id: I21b21ebb357eab61e36c080c328291ed20b8eb8f Reviewed-on: https://chromium-review.googlesource.com/497749 Reviewed-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>