Add a GetVariableInfo helper method. 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/206566 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Nicolas Capens <capn@chromium.org>