expose new tight-bounds method on SkPath

BUG=skia:

Change-Id: Ie50df49c1758af203042a84dc2cd505046373d2c
Reviewed-on: https://skia-review.googlesource.com/7996
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
5 files changed