This prevents overflow issues in the HLSL translator and some drivers. The
limit it hard-coded to 65536 to be larger than the Shader Model 5 register
limit (4096) to account for register allocation optimizations and future
hardware.

BUG=379799

Change-Id: I20f05c9dd230fbfc1c92af52533cd2b50f2ff994
Reviewed-on: https://chromium-review.googlesource.com/202939Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Nicolas Capens <nicolascapens@chromium.org>