Take any array sizes that have been explicitly specified in the shader
text into account, and only set the ones that are unsized according to
the arguments.

BUG=angleproject:2125
TEST=angle_unittests

Change-Id: I37d08a86c25f7cd4f3ce5689f2c9fad444e7d5ad
Reviewed-on: https://chromium-review.googlesource.com/738141
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>