The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/e88e61b4507a2f249987519f2ea03a9c4832b1f5

commit e88e61b4507a2f249987519f2ea03a9c4832b1f5
Author: Jeffrey Li <lijeffrey@chromium.org>
Date: Tue Aug 28 19:42:05 2018

[Findit] Flake Analyzer - Improved fallback logic for mapping commit positions to builds

Temporary workaround to assist in the fallback logic for when IsolateTargets are unavailable.
Currently an upper_bound_build_number is used to assist in searching buildbot, however is
capped at 500 builds below the triggering build number. In many cases, lookback will go further
back than 500 builds leading to exceptions unnecessarily. Until all builds are on LUCI and
indexed, falling back to build_number is still necessary in some cases.

1. Preserve build_number when BuildInfo is used when IsolatedTargets are unavailable and store
   to Flakiness (eventually converted to DataPoint).
2. Use a dynamic upper bound to tart searching nearby based on all available data points, choosing
   the lowest that has commit position greater than the requested, instead of just the
   triggering build number to avoid running off the 500 build window prematurely.

Bug:  877691 
Change-Id: I89899c7ec042f8f0d99ddc1c8d6c113a6bc95677
Reviewed-on: https://chromium-review.googlesource.com/1189087
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Jeffrey Li <lijeffrey@chromium.org>

[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/services/flake_failure/test/flakiness_util_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/services/flake_failure/test/data_point_util_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/test/update_flake_analysis_data_points_pipeline_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/services/flake_failure/data_point_util.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/model/flake/test/master_flake_analysis_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/test/determine_approximate_pass_rate_pipeline_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/next_commit_position_pipeline.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/test/get_isolate_sha_pipeline_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/model/flake/master_flake_analysis.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/analyze_flake_pipeline.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/get_isolate_sha_pipeline.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/dto/flakiness.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/test/save_flakiness_verification_pipeline_test.py
[modify] https://crrev.com/e88e61b4507a2f249987519f2ea03a9c4832b1f5/appengine/findit/pipelines/flake_failure/determine_approximate_pass_rate_pipeline.py