This also makes BlitGL work correctly on OpenGL ES (provided vertex
arrays are available)

BUG=angleproject:1356

Change-Id: Icb7cef35bebfe6672220aa0b312ab89187dbf585
Reviewed-on: https://chromium-review.googlesource.com/412452
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>