LGTM. Since you don't actually implement most of that public API in our emulation library, I believe you get a compile error even in dev mode if client code tries to call it. So I would expect that (unless you add those functions to the JRE in the future) those methods will never get called from a client thread.
http://gwt-code-reviews.appspot.com/437801/show -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
