Arguments object has @@iterator

R=arv@chromium.org, verwaest@chromium.org, rossberg@chromium.org
BUG=v8:3391
LOG=N
TEST=mjsunit/harmony/arguments-iterator.js

Review URL: https://codereview.chromium.org/342453002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23341 ce2b1a6d-e550-0410-aec6-3dcde31c8c00