While Desktop GLSL supports the Coarse and Fine flavours, GLSL ES does
not. For now, emit dFdx/dFdy in all cases for ES, but excluding the
Coarse and Fine flavours via validation is also an option.
Bug: tint:1445
Change-Id: Iaac589f72043b5547e9141a6e870c1fd49631f6f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/82142
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>