This refactoring reduces code duplication and moves functionality that is
not immediately related to the language grammar out of glslang.y.

BUG=angle:911

Change-Id: If5e225461890ed542dee01905829df1c9a6f5e27
Reviewed-on: https://chromium-review.googlesource.com/248570Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>