Add --gpuThreads support to skpbench.py (take 2)

Change-Id: Ie946ff339c4e04bb866545ad60c2ab77bae85417
Reviewed-on: https://skia-review.googlesource.com/136175
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed