Extract ToolUtils::sniff_paths

Makes the path sniffing code from BisectSlide reusable.

Change-Id: I21c1e752590359c557c35804e5d5044d8041a308
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/460637
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
4 files changed