[graphite] GridBoundsManager

And a little bit of unit tests and benchmarking...

Change-Id: I56252846c2c00f35e70472e5d8272717d6ec4b25
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/545897
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
6 files changed