Add ASTC compressed texture format info to the GL layer. BUG=angleproject:1185 Change-Id: Ie723687e0289812d6c2306589911b548ac321e22 Reviewed-on: https://chromium-review.googlesource.com/308491 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>