Perf Tests: Call finish every step in calibration. Calibration is only supposed to take one second of warmup time. Instead we were queuing up a large amount of GPU work and then janking on the finish call at the end of calibration. Fix this by calling glFinish repeatedly during calibration. Bug: chromium:1136900 Change-Id: Idb2fefe17fcb9acbe688cff5a36f051732fc5b59 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2483462 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>