BUG=angleproject:1729
TEST=dEQP-GLES31.functional.ssbo.layout.*
     dEQP-GLES31.functional.compute.basic.atomic_counter*

Change-Id: Ic78c0f089fd539c0b1064e8405d63505456dbc01
Reviewed-on: https://chromium-review.googlesource.com/777958
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>