The trace tests were including the startup time in their calibration
calculations. Then was forcing them to always render one step. This
fixes the calibration to attempt to get a more consistent measurement.
The trace tests now render many more steps than they did before. It
should increase the stability and decrease variance in our measurements
as they will be runnnig many more frames than before.

Also adds a verbose logging flag to help debugging.

Noticed this bug when working on the trace test offscreen mode.

Bug: angleproject:4845
Change-Id: Iff0c987008a935e7051fca34ef12f4433eb46092
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2300205Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>