The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/ac40b9383ea8f0c1d9dc81af0acc137f61c17784

commit ac40b9383ea8f0c1d9dc81af0acc137f61c17784
Author: Brandon Wylie <wylieb@chromium.org>
Date: Wed Apr 11 23:01:23 2018

[Findit] Flake Analyzer - Use upper_bound - 500 for the lower bound.

This works since we only look back 500 builds by default. Upper bound
in this case is the detected build number which is our starting point
for all analyses.

Bug:  823427 
Change-Id: I8947dbc81ff9ae001df2f29d5f902d35df790507
Reviewed-on: https://chromium-review.googlesource.com/1008280
Commit-Queue: Brandon Wylie <wylieb@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>

[modify] https://crrev.com/ac40b9383ea8f0c1d9dc81af0acc137f61c17784/appengine/findit/pipelines/flake_failure/next_commit_position_pipeline.py
[modify] https://crrev.com/ac40b9383ea8f0c1d9dc81af0acc137f61c17784/appengine/findit/services/step_util.py
[modify] https://crrev.com/ac40b9383ea8f0c1d9dc81af0acc137f61c17784/appengine/findit/waterfall/flake/regression_range_analysis_pipeline.py
[modify] https://crrev.com/ac40b9383ea8f0c1d9dc81af0acc137f61c17784/appengine/findit/services/test/step_util_test.py
[modify] https://crrev.com/ac40b9383ea8f0c1d9dc81af0acc137f61c17784/appengine/findit/pipelines/flake_failure/get_isolate_sha_pipeline.py