Don't query this as an Impl method, since it exists on the GL level. Also some related refactorings and cleanups. BUG=angleproject:1123 Change-Id: I3610bc0db2bcaa96408506e06a65a2f4dab93150 Reviewed-on: https://chromium-review.googlesource.com/293761Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>
