Chromium doesn't ship binaries to end users. Linux distros that have chromium build it from source. But I suspect that they are probably going to switch to clang as the recommend compiler for development.
AFIAK, Chromium core devs are all Google employees, and their code makes up the base for Chrome, although Chrome is Google branded and includes other features such as usage tracking. I found a talk given in 2011 by two Chromium devs about using clang, which seems to point to nearly the same increase in build performance along with a few other reasons they like using clang. Anyways, seems like they've been using clang for a while. http://llvm.org/devmtg/2011-11/Weber_Wennborg_UsingClangInCh...
