Reduce --use-angle spam in TracePerfTest. Instead of recalculating the back-end for every trace, we can do it once in the test instantiation and pass the results around. Bug: angleproject:7755 Change-Id: I492c639d91ee6ad6a325cff090813aaeb900b2d8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3971080 Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Cody Northrop <cnorthrop@google.com>