Changed the debugger break handling to support situations where there are no stack frames. This can happen when an exception is thrown when compiling code.

This is related to Chromium issue 5349 (http://code.google.com/p/chromium/issues/detail?id=5349).
Review URL: http://codereview.chromium.org/13720

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@959 ce2b1a6d-e550-0410-aec6-3dcde31c8c00