I think we'll only need Vulkan. But in any case, the GL code doesn't
build, so disable it for now.

Bug: chromium:808287
Change-Id: I08f8cd09e67d91c08b7632e54bbdc6a11ee57014
Reviewed-on: https://chromium-review.googlesource.com/c/1298381Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>