Fix issue with Map/SetIterator and types

BUG=v8:3281
LOG=N
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/246993003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20893 ce2b1a6d-e550-0410-aec6-3dcde31c8c00