Make GrClip.h private

BUG=skia:

Change-Id: I4aa3c2707811ece3a63d161035e316c3bbc1cd15
Reviewed-on: https://skia-review.googlesource.com/9482
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
20 files changed