Rendering from disabled attributes is implemented using small dynamic
buffers. The buffers use a stride of zero so the same vertex data is
pulled for every index.

This fixes all the disable attribute tests in dEQP.

Bug: angleproject:2444
Change-Id: I04fe139076da3e3ff723bed8eb17e333b4cb0ddf
Reviewed-on: https://chromium-review.googlesource.com/1136664
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>