This method replaces the similar logic in storing uniforms,
varyings, and interface blocks when collecting variable info.
We can also re-use this method for both GLSL and HLSL programs.

BUG=angle:466

Change-Id: Ie6c13abe0f09f38b2f9b36e117caae4833eaccbf
Reviewed-on: https://chromium-review.googlesource.com/206566Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>