These variable types apply across shader types. Either we'll want a
way to cache them after we query them, or we'll do a pre-parse pass
similar to our current Chromium GLSL to GLSL pre-pass where we store
the variables in ANGLE. In either case, they're shared across GL
implementations so make sense as queries from gl::Shader.

BUG=angle:731

Change-Id: I23f5541423abb4af87a2bc2fc1e9f4047fd2ff90
Reviewed-on: https://chromium-review.googlesource.com/214870Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>