This combination is not allowed by the formal grammar in the ESSL 3.00
spec, and should still be disallowed in ESSL 3.00 shaders even though
the shader parser now implements the more flexible ESSL 3.10 grammar.

BUG=angleproject:1507
TEST=angle_unittests

Change-Id: I766a468fd7314c7e60e020b5b204aa6950263633
Reviewed-on: https://chromium-review.googlesource.com/381933Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>