Add Graphite support for runtime effect tests.
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 <509afb0bfbb23ecaaf1fb3323209f531b45e75a6@google.com>
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia