Add generic factory function to GrFillRectOp

Bug: skia:
Change-Id: Iaa56cdb8107dc278e585807ec10aeae53150b97a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/214720
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed