This makes it possible to build V8 without JavaScript debugging support in debug mode.

BUG=http://code.google.com/p/v8/issues/detail?id=454
Review URL: http://codereview.chromium.org/242048

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2983 ce2b1a6d-e550-0410-aec6-3dcde31c8c00