This is enough to support the operations in GLSL output. HLSL output will
likely require additional work to support this.

BUG=angleproject:941

Change-Id: I728d511ab07af94bc3382dc2796c1e9ac79d1442
Reviewed-on: https://chromium-review.googlesource.com/260801Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>