Not yet, but they're working on a solution using the LLVM bitcode format:

http://nativeclient.googlecode.com/svn/data/site/pnacl.pdf http://www.chromium.org/nativeclient/native-client-documenta...

Not truly machine-independent. How can you run x86 code on an ARM architecture, and vice-versa? Although if they do have this feature in Chromium it could make a huge difference in performance of web apps.