Add a test for sampler as a function parameter
Add a test for sampler as a function parameter

This adds some coverage for samplers that's missing from dEQP.

The test shader passes a sampler to an user-defined function, samples
the texture there and sets the returned sample to gl_FragColor. The
test then checks that the shader result is correct.

BUG=angleproject:1261
TEST=angle_end2end_tests

Change-Id: I2cc511e591a4af01515c6fb38fd43c5f15337bcb
Reviewed-on: https://chromium-review.googlesource.com/321622
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Zhenyao Mo <655bdf1d95ff956cd68886dd9e86ee5e987c9dbb@chromium.org>
Tested-by: Olli Etuaho <38ae6c0e2772a20e8e989f80cb8c99d274e44242@nvidia.com>

ppy/angle,domokit/waterfall,ecoal95/angle,ecoal95/angle,mlfarrell/angle,ppy/angle,mikolalysenko/angle,ecoal95/angle,domokit/waterfall,mikolalysenko/angle,ppy/angle,mikolalysenko/angle,ecoal95/angle,ecoal95/angle,mlfarrell/angle,mikolalysenko/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,mlfarrell/angle,MSOpenTech/angle,MSOpenTech/angle,mlfarrell/angle