The script reads the list of tests from the restricted traces JSON and
runs angle_perftests once for each test. Running the tests in a batch
seems unstable on some platfroms so running each test separately works
around that limitation. It does not yet interact with Skia Gold. The
Gold integration will come later once this basic skeleton is running
on the bots.

Also updates the perf tests to exit more quickly with --one-frame-only.
This will speed up the screenshots.

Example run with trigger.py:
https://chromium-swarm.appspot.com/task?id=4ecb985330a33910

Bug: angleproject:4090
Bug: b/168049670
Test: tested with trigger.py
Change-Id: I52820dfba2acfbc5d638673c37297877e8476adb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2417641
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>