[graphite] Set up unit testing system

Bug: skia:12466
Change-Id: I401a185d818a964327d323b9ebcd0850ec0b1c9b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/457318
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
18 files changed