Fix bug in __proto__ assignment transition cache where we forget the next enumeration index resulting in wrong iteration order.
Review URL: https://chromiumcodereview.appspot.com/10515006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11706 ce2b1a6d-e550-0410-aec6-3dcde31c8c00