The test generates a texture containing random data and then blurs it in
a fragment shader using nearest neighbor sampling. The test is
specifically designed to test overhead of GLSL's builtin texture*()
functions that may result from how ANGLE translates them on each backend.

BUG=angleproject:1261
TEST=angle_perftests

Change-Id: I188fa8c07e609b7f371e587358f913b506bd7d44
Reviewed-on: https://chromium-review.googlesource.com/319382Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tryjob-Request: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>