Move transformation of clip elements to SkClipStack::Element

Change-Id: Ia6ff3fdc927e33dbd28ccfb345859594289d0690
Reviewed-on: https://skia-review.googlesource.com/36820
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
3 files changed