This uses the fact that if a map stayed the same then the object
still passes the type check. A new builtin is added to handle the
API call in this case.

Review URL: http://codereview.chromium.org/573003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3825 ce2b1a6d-e550-0410-aec6-3dcde31c8c00