move SkPathRef.h into private

Bug: skia:
Change-Id: I3370c594301ae833ec1fe3cb16ac544e5b2128e8
Reviewed-on: https://skia-review.googlesource.com/18982
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
4 files changed