read-only property in the prototype chain.  Stores should only be
ignored if there is a read-only property on the object itself.
Review URL: http://codereview.chromium.org/42508

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1584 ce2b1a6d-e550-0410-aec6-3dcde31c8c00