This is implemented as a compiler option which is enabled by default
when outputting to desktop GLSL version 130 and greater, which does
not support this #pragma in fragment shaders. As a workaround, and for
better compatibility on desktop OpenGL drivers, this pragma is also
flattened into the outputs of vertex shaders, and the inputs of ESSL
1.00 fragment shaders.

TEST=conformance/glsl/misc/shaders-with-invariance.html with --enable-unsafe-es3-apis
BUG=629622, angleproject:1293

Change-Id: Ib040230915e639971505ed496d26e804c9d64e68
Reviewed-on: https://chromium-review.googlesource.com/361792Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>