Google's Goma client is now open source

"Goma is a distributed compiler service for open-source project such as Chromium and Android. It's some kind of replacement of distcc+ccache."

https://chromium.googlesource.com/infra/goma/client/

I know that Opera at least, had been using icecream (https://github.com/icecc/icecream) internally to do distributed builds, and occasionally the main repo would make a modification to the build system that would break it. One time this actually resulted in the discovery of a bug in the llvm project (https://bugs.chromium.org/p/chromium/issues/detail?id=778209). Hopefully external teams that are building chromium will have this pain point alleviated. :)