Full scale adoption of LLVM/Clang/LLDB/Compiler-RT/libc++abi/libc++ will be adopted in WebKit. You can bank on it.
Google is a huge contributor to these projects and is pushing them just as hard as Apple (to the point that I've seen some of Google's engineers claim Clang as "their" compiler even though the initial code drop and continued release management is by Apple-employed engineers). Google has been doing a lot specifically with its WebKit (now Blink) code and the Clang family of projects. Most Google developers I've worked with use OS X as their primary dev machines with Windows/Linux VMs and secondary boxes just for building and testings the ports. So everything you say is true but essentially irrelevant. Blink is less likely to ever _only_ work with Clang, but strong integration with and support for Clang and related tools will remain a top priority for Blink. I expect to see more use of Clang tools and analysis in Blink as time goes on since Google's dev tools team is writing most of those tools, often explicitly at the behest of Google's Chromium team.