Add bisect_roll tool

1. Loads the list of commits which have not yet rolled.
2. Loads the recent roll attempts.
3. Suggests a commit to try.
4. Uploads a roll CL at the commit specified by the user.

Bug: skia:
Change-Id: I68a7f6dbbca638cc9f17bad4eed71e889fe43b6e
Reviewed-on: https://skia-review.googlesource.com/93580
Commit-Queue: Eric Boren <borenet@google.com>
Reviewed-by: Ravi Mistry <rmistry@google.com>
3 files changed