Add ASTC compressed texture format info to the GL layer. BUG=angleproject:1185 Change-Id: Ia0bbe85fe8fa2b6a55289ff291f30e215d7a3ba9 Reviewed-on: https://chromium-review.googlesource.com/301146 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>