This paves the way for perf tests that measure GPU performance.

Bug: angleproject:2999
Change-Id: I9d49d3e1256d8d18514885ae63264a5fbc5c29d1
Reviewed-on: https://chromium-review.googlesource.com/c/1436839
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>