When running with "--one-frame-only" we can also skip the test warmup.
Also we can reduce the internal iteration count to 1 to make the tests
as fast as possible.

Bug: angleproject:2923
Change-Id: I2f82ae0dd237767ea7b15074e459ed1094ba9943
Reviewed-on: https://chromium-review.googlesource.com/c/1308737Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>