Ensure that a warning is generated if the shader tries to set a global
layout qualifier. Since a num_views layout qualifier is the only valid
global layout qualifier in GLSL ES 1.00, it's sufficient that
checkCanUseExtension() that generates the warning is called for
"num_views" specifically. Parsing "layout" or "in" storage qualifier
may use the simpler isExtensionEnabled() check that doesn't generate a
warning.

BUG=angleproject:2238
TEST=angle_unittests

Change-Id: I19caff7be9cb4f53c581b5f5526b7cade08469d6
Reviewed-on: https://chromium-review.googlesource.com/803577Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>