move patheffect virtuals to protected and rename

- change filterPath to safely handle if src and dst are aliases

Bug: skia:8254
Change-Id: I125d19404ca0a610f73271abb5c5455d1d50f9ed
Reviewed-on: https://skia-review.googlesource.com/147466
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Mike Reed <reed@google.com>
20 files changed