This is a reland of 6034941cc2
Original change's description:
> Add SkRuntimeBlender class.
>
> This class is returned by SkRuntimeEffect::makeBlender when a runtime
> blend is returned. SkRuntimeBlendBuilder is also added as a convenience
> class to simplify creation and uniform setup.
>
> Our ability to add tests is limited in this CL because the SkPaint does
> not contain an SkBlender yet. We do have one test which builds an
> SkBlender, but there's not much we can do with it. Testing will be
> bulked up in the next CL.
>
> Change-Id: Ib2d7d04186690ec0d2238fc990a19d9e6b786ce3
> Bug: skia:12080
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/417006
> Commit-Queue: John Stiles <johnstiles@google.com>
> Auto-Submit: John Stiles <johnstiles@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>
Bug: skia:12080
Change-Id: Ie41be141ba3787452f9d5c72946ebc748a5d6176
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/419160
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
491282486e