Also adds a new test in GLSLTest to validate the initialization of
a struct on the same line as its declaration.

Bug: angleproject:2459
Change-Id: Ib37e20378f8ec76541db26392663bcba03390756
Reviewed-on: https://chromium-review.googlesource.com/1017340
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>