The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/8dace2766077a27e07b4b6d90c50664aa3812e90

commit 8dace2766077a27e07b4b6d90c50664aa3812e90
Author: Don Garrett <dgarrett@google.com>
Date: Tue Jul 24 19:44:16 2018

gen_luci_scheduler: Add branched build config support.

This adds chromeos_config.BranchScheduleConfig, which defines
scheduling information for branched configs. These are special
"scheduler only" configs.

gen_luci_scheduler is updated to include the branched configs when
creating the schedule file.

As an example of usage, this adds scheduling for the R69 release
branch, including PFQ builders.

BUG= chromium:859203 
TEST=run_tests + manually examining gen_luci_scheuler output.

Change-Id: I0f16eb2c37223db4d536c6855e0417f77686dafb
Reviewed-on: https://chromium-review.googlesource.com/1146992
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>

[modify] https://crrev.com/8dace2766077a27e07b4b6d90c50664aa3812e90/config/chromeos_config.py
[modify] https://crrev.com/8dace2766077a27e07b4b6d90c50664aa3812e90/scripts/gen_luci_scheduler.py
[modify] https://crrev.com/8dace2766077a27e07b4b6d90c50664aa3812e90/scripts/gen_luci_scheduler_unittest.py