This sources the trace list from a json file and uses that to make the
"glue" that works with each individual trace test.

Bug: angleproject:4590
Change-Id: I40808cbd0e00f9ed01f93c4cfbd678401db3fec0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2168539
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>