Add GM to exercise "powerless" hue cases of gradient interpolation

https://csswg.sesse.net/css-color-4/#interpolation-missing

We currently draw this GM wrong. Next step will be to implement
(roughly) the CSS logic for carrying values forward to fill
in missing/powerless components.

Bug: chromium:1462612
Change-Id: Id5084e7039f856efe2f3e4314c5934cb3a2a0239
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/749877
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed