add mad() and shuffle() to SkVx

Change-Id: Ie3e5b353f84e74d398a5350dc0baff5541789119
Reviewed-on: https://skia-review.googlesource.com/c/189982
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
2 files changed