The actual code changes LGTM, but I am skeptical about the performance benefits of guarding all the ones that do nothing more than string concats. If that is really too expensive, then virtually no log call should be unguarded, and we should just require callers to insert their own guards and remove the check from log/branch.
Before committing the guards around just string concats, I would like to see some measurements that suggest it is worth the cost of cluttering up the code. http://gwt-code-reviews.appspot.com/1426802/ -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
