There is an optional parameter to the function, with default value being a null handle. We then check that this is a flat string.
Review URL: http://codereview.chromium.org/7850011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9184 ce2b1a6d-e550-0410-aec6-3dcde31c8c00