Share GP implementation between GrFillRectOp and GrTextureOp

Bug: skia:
Change-Id: I6c71dac4cf88f274a39f121f0b5315e6c5b914c8
Reviewed-on: https://skia-review.googlesource.com/c/173700
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
4 files changed