tagged case. I couldn't find a way to test the double case yet so I'm
leaving that unimplemented for now.

Review URL: http://codereview.chromium.org/6347007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6411 ce2b1a6d-e550-0410-aec6-3dcde31c8c00