Return shader variable information using GLenum values.

Instead of duplicating GL header define values, explictly return
GLenum for variable queries in the shader inspection API. This
reduces the duplicate defines in the shader compiler header.

BUG=angle:466

Change-Id: Iddaaff597b188251fa2e546f352bf77ab3ac43bc
Reviewed-on: https://chromium-review.googlesource.com/205860
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>
32 files changed