Struct definitions are not allowed as a function parameter type now.
This is specified in ESSL 3.00.6 section 12.10. ESSL 3.00.6 section
6.1.1 contradicts this, but that seems like a mistake, it's been fixed
in subsequent spec versions.

BUG=angleproject:2225
TEST=angle_unittests

Change-Id: I6b97d120c440f0c0a45d31bbfaf292fb497160ce
Reviewed-on: https://chromium-review.googlesource.com/754606Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>