Includes the following fixes:

* Removes obsolete global variable.
* Disables trace event collection when trace events disabled.
* Fixes calibrated steps getting stuck after first test.
* Scale calibrated steps with actual time after glFinish.

Should fix a few crashes and timeouts with the perf tests.

Bug: angleproject:2923
Change-Id: I9ba1c042dee31cf2400ccbeedca0d497ed52fb12
Reviewed-on: https://chromium-review.googlesource.com/c/1343677Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>