Introduce a "null" GL renderer for this specific benchmark, which
does not do any work on drawArrays and drawElements. We could use
the same kind of trick for buffer and texture updates, if we need
it. This gives us a good baseline for comparing GL and D3D perf.

BUG=angleproject:1040

Change-Id: I4bf7c75df01932de45ddd0a4e42e8fc82f15e37e
Reviewed-on: https://chromium-review.googlesource.com/276192Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>