Allow explicit coords to be plumbed through blender functions.

This allows us to support a chain of FPs that includes both blenders
and matrices.

Change-Id: Ic8a4ea3eb24b7fd45552607be196461e999f03ea
Bug: skia:12257
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/434656
Reviewed-by: Brian Salomon <bsalomon@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
2 files changed