Initial definition of fill rect op

Bug: skia:
Change-Id: Ie0c99eb5163501853d1adc885bd3841f90a71924
Reviewed-on: https://skia-review.googlesource.com/c/163486
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
13 files changed