Use the CollectVariables path on the HLSL translator. This approach consolidates our two methods, and lets us reuse the same code for both methods of variable collection. BUG=angle:466 Change-Id: Ie92f76ff0b6d0d0dbfd211a234d0ab86290fa798 Reviewed-on: https://chromium-review.googlesource.com/213504 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Nicolas Capens <capn@chromium.org>