Perf Tests: Use specified trial time for warmup. When the user specifies a trial time, use this for the warmup time instead of using the calibration time. This will give a longer warmup time on our test infra and should help stabilize perf testing scores on our bots. Bug: angleproject:7671 Change-Id: I65fb8a7ae1f684d3f7834613d8341d17bd2df00f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3933315 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>