For-of calls [Symbol.iterator]() on RHS to get iterator

R=rossberg@chromium.org
BUG=http://code.google.com/p/v8/issues/detail?id=2735
LOG=N

Review URL: https://codereview.chromium.org/332663004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21820 ce2b1a6d-e550-0410-aec6-3dcde31c8c00