The only error in the test should be the non-integer index. gl_FragColor
should be used correctly.

BUG=angleproject:1254
TEST=angle_unittests

Change-Id: I0b7a36be5485661cc03bf2c476aaacae5d3b6e76
Reviewed-on: https://chromium-review.googlesource.com/320280Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>