This also touches the extension EPs for ES2.

BUG=angleproject:747

Change-Id: Iaa04d97465e518f6b0496e64bc7a737914709b8f
Reviewed-on: https://chromium-review.googlesource.com/637124Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>