In several places we were using variable query methods that
were duplicated between the old SH enums and the corresponding
GL enums. We can use the common GL enum versions now.

BUG=angle:466

Change-Id: Ib8797fe6bc75828e05aed37b1f5fbd4b9ba03d22
Reviewed-on: https://chromium-review.googlesource.com/205594Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>