I think it comes with it, but I'm not sure. I haven't installed the preview yet - the warnings about only using a test machine to avoid damage kinda turned me off from just trying it immediately on my personal computer.
No. Visual Studio build of clang++ links with the Microsoft library; native C++ programs can be built with it.
Not Chrome (or Chromium) though. Chrome releases on Windows are built using the Microsoft compiler; other tool-chains (on Windows) are not supported by the Chromium build framework.