move some of patheffect internals into private

BUG=skia:

Change-Id: I00da9d38f16fb20f31e025dd817c5d430466a1d0
Reviewed-on: https://skia-review.googlesource.com/9236
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed