Implement Sk4f min/max

Bug: skia:
Change-Id: Icf235dea81e9f125c1c8590ec87cb3591393036c
Reviewed-on: https://skia-review.googlesource.com/120281
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed