Add Graphite support for runtime effect tests.

One of the 18 tests is disabled because the paint color does not pass
through when evaluating a null child effect. (This also affects GMs
`null_child_rt` and `default_color_rt`.) A fix is on deck at
http://review.skia.org/583637.

Change-Id: I90255536ffe990311d16d41a2fe48b491e432f21
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/583636
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
1 file changed