keep a running tally of consecutive number of successful or failed builds

This CL adds a google-storage backed streak counter, which counts the
number of consecutive passed or failed builds for each commit queue
builder. This is done by extending the functionality of GSCounter, and
adding a step to ReportStage which updates the gs-backed counter.

TEST=Unit tests pass. cbuildbot --buildbot --debug

Change-Id: Ib069f8559dfb6b756c6f30ee73b929ab9dd0294f
Reviewed-by: Aviv Keshet <>
Tested-by: Aviv Keshet <>
Commit-Queue: Aviv Keshet <>
4 files changed