Same for WeakMap/WeakSet

https://bugs.ecmascript.org/show_bug.cgi?id=3111

BUG=v8:3508
LOG=Y
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/466003002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23091 ce2b1a6d-e550-0410-aec6-3dcde31c8c00