This change makes us compatible with Safari on not throwing when trying to add a property to a non-extensible object. 
Review URL: http://codereview.chromium.org/6712059

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7379 ce2b1a6d-e550-0410-aec6-3dcde31c8c00