BUG=angleproject:2070

TEST=deqp/functional/gles3/shaderderivate_dfdx
TEST=deqp/functional/gles3/shaderderivate_dfdy
TEST=deqp/functional/gles3/shaderderivate_fwidth

Change-Id: I4e10343036a813c122ca41913324051b5c02e785
Reviewed-on: https://chromium-review.googlesource.com/538861Reviewed-by: Jamie Madill <jmadill@chromium.org>