These methods can obviate the need for glGen/Delete calls in tests.

BUG=angleproject:1407

Change-Id: Ied571e48db92bd1d4f4089d91a95e7c7fafcfcaf
Reviewed-on: https://chromium-review.googlesource.com/350904Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>