We have builders that have been waiting for more than a week there:

Builder link:
https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Mac10.12%20%28retina%29

Maybe build51-b1 might just need to be restarted for some reason?
https://uberchromegw.corp.google.com/i/chromium.webkit/buildslaves/build51-b1

Note, the bug for migration of this builder is bug 821647, but migration hasn't started yet (I think) for this builder.

So, the next step for this I think is for Labs team to restart build51-b1.

It's back up now, needed a hard power-cycle. Looks like this bot has a history of going offline, and the hardware was already replaced once, to little avail, it seems.

Thanks! I guess we have lots of other Macbook Pros, but this one is particularly more likely to go offline, and this one is also a bit different than the others?

Actually, GPU macbooks also seem to go offline occasionally, so this might be the same symptom here. It's almost like they get into a bad state after running some tests. We regularly need to revive them, but since GPU is all swarming, they can tolerate some small percentage being offline at a time.

 Issue 833384  has been merged into this issue.