We might need to revisit this when we implement other GL
back-ends.

BUG=angle:773

Change-Id: I6e742254bd0df8cc899ea02a523992b4d66dfd68
Reviewed-on: https://chromium-review.googlesource.com/229061Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>