It is frequently used inside our builtins and is implemented purely
by HIR instructions: a smi check, an instance-type check and an
in-object property store for storing to the value field.
Review URL: http://codereview.chromium.org/8507016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9952 ce2b1a6d-e550-0410-aec6-3dcde31c8c00