add TrimPathEffect

Bug: skia:
Change-Id: I453fb81ded4435b33567e9c8a6f3abe9535d687f
Reviewed-on: https://skia-review.googlesource.com/112820
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
7 files changed