This file was missing on GCC builds.

BUG=angle:773

Change-Id: I6222b5ee563d64967d878c422abd464c8c92e646
Reviewed-on: https://chromium-review.googlesource.com/231855Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>