A new callback have been added which - if set - will be called to dispose of external string resources passed from the embedder to the V8 engine.
Review URL: http://codereview.chromium.org/2645004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4805 ce2b1a6d-e550-0410-aec6-3dcde31c8c00