The ref already exists:
https://chromium.googlesource.com/v8/v8/+/canary

It is updated by an internal builder:
https://uberchromegw.corp.google.com/i/internal.client.v8/builders/v8_canary_detector

The bot is not using what is actually pushed out, i.e. what omahaproxy would show, but the latest candidate. That's usually a good approximation.

Adding such a builder to chromium shouldn't be too hard, but this might additionally require:
- Better documentation and maintenance of the canary ref updater. If it breaks, troopers need to know what to do.
- A corresponding CI bot. One exists, but in V8 territory:
https://build.chromium.org/p/client.v8.chromium/builders/Linux%20V8%20API%20Stability