added support for sk_ClipDistance

Change-Id: I9ea202679211b98cf98165c8609f24f9b4e14b66
Reviewed-on: https://skia-review.googlesource.com/8247
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
5 files changed