The multiview transform feedback test was not compliant with the GLES
spec for transform feedback. The issue had to do with this part of
section 2.15.2 of GLES 3.0.5 spec:

"The error INVALID_OPERATION is also generated by
BeginTransformFeedback if no binding points would be used, either
because no program object is active or because the active program
object has specified no output variables to record."

Fix this.

BUG=angleproject:2184
TEST=angle_end2end_tests on NVIDIA 387.92 drivers

Change-Id: I24816d2c24df0072179f21ead892bd2c9ba696d2
Reviewed-on: https://chromium-review.googlesource.com/718702
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>