The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/c4cc4b861fb97e6f652e3068686ff4e6aaa2c5f2

commit c4cc4b861fb97e6f652e3068686ff4e6aaa2c5f2
Author: Jeffrey Li <lijeffrey@chromium.org>
Date: Mon Mar 19 19:44:46 2018

[Findit] Flake Analyzer - Fixing lookback to use exponential search

lookback_algorithm.py itself is fine, but the root cause is the calling
code failing to sort the data points beforehand thus the lookback
algorithm will always use the first two data points (when step size is
at its smallest) to determine the next step size.

1. Have the calling code sort the data points properly before passing
   to lookback_algorithm.
2. Add an assert in lookback_algorithm that ensures the data points are
   sorted.

Change-Id: I2b62ffee27b9d99b5ff266406fe9641275bfbe84

Bug:  822395 
Change-Id: I2b62ffee27b9d99b5ff266406fe9641275bfbe84
Reviewed-on: https://chromium-review.googlesource.com/969101
Reviewed-by: Brandon Wylie <wylieb@chromium.org>
Commit-Queue: Jeffrey Li <lijeffrey@chromium.org>

[modify] https://crrev.com/c4cc4b861fb97e6f652e3068686ff4e6aaa2c5f2/appengine/findit/pipelines/flake_failure/next_commit_position_pipeline.py
[modify] https://crrev.com/c4cc4b861fb97e6f652e3068686ff4e6aaa2c5f2/appengine/findit/services/flake_failure/lookback_algorithm.py