The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/02cb7e18c212e459e7156a03832646ed837d523d

commit 02cb7e18c212e459e7156a03832646ed837d523d
Author: Jeffrey Li <lijeffrey@google.com>
Date: Wed Jan 10 06:51:40 2018

[Findit] Flake Analyzer - New lookback algorithm independent of build numbers

1. Implement a new lookback_algorithm.py module under services/flake_failure
   so as not to disturb the existing lookback_algorithm under waterfall/flake.
   https://chromium.googlesource.com/infra/infra/+/master/appengine/findit/waterfall/flake/lookback_algorithm.py
2. Implement quadratic search by commit position.
3. Get rid of all references to builds/build numbers from lookback_algorithm - this
   services module should have no concept of builds.
4. Swap linear search forward in favor of exponential search backward: Flakiness is most
   relevant the more recent the CL, so always bias searching from the right (later commits)
   instead of the left (earlier commits) whenever possible to avoid obsolete culprits.
5. Bisect for nonexistent tests to find when the test was added.
6. Deprecate checks for dives in pass rates (historically yields false positives)
7. Overall massive overhaul/cleanup of old lookback_algorithm.py


Bug:  797458 
Change-Id: I956f97cab61ce0c6dff2c901d72285b261f2ba1b
Reviewed-on: https://chromium-review.googlesource.com/843486
Commit-Queue: Jeffrey Li <lijeffrey@chromium.org>
Reviewed-by: Brandon Wylie <wylieb@chromium.org>

[add] https://crrev.com/02cb7e18c212e459e7156a03832646ed837d523d/appengine/findit/services/flake_failure/test/lookback_algorithm_test.py
[add] https://crrev.com/02cb7e18c212e459e7156a03832646ed837d523d/appengine/findit/services/flake_failure/lookback_algorithm.py