KHR_debug from the GL drivers was generating a lot of spam.

BUG=angleproject:1925

Change-Id: I89568ea2bec3afb629f86c25d9e80aad1dbe79f8
Reviewed-on: https://chromium-review.googlesource.com/450857Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>