buildbot master chromium.swarm triggers:
- ToT chromium builds on Ubuntu/OSX/Windows/Android to confirm the infrastructure works.
- heartbeat as a signal if anything goes wrong.

It's an easy builder to convert to a pure LUCI setup, as there's no try job, and it's purely time based (let's say one chromium build every 1.5 hour, one heartbeat every minute)

It's triggering config can live in the infra.git repository.

Some references for myself:
https://chromium.googlesource.com/chromium/src/+/infra/config/cr-buildbucket.cfg
https://chromium.googlesource.com/infra/infra.git/+/infra/config/luci-scheduler-dev.cfg
https://chrome-internal.googlesource.com/infradata/config.git/+/master/configs/cr-buildbucket-dev/swarming_task_template_canary.json