Improve tests for debug API to check behavior of JS_RETURN and DEBUG_BREAK_SLOT relocations.

Review URL: http://codereview.chromium.org/3058049

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5180 ce2b1a6d-e550-0410-aec6-3dcde31c8c00