WeakMap/WeakSet: Add test for non object keys

Add test for non object keys in the iterable passed to the constructor.

BUG=v8:3399
LOG=Y
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/451033003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23090 ce2b1a6d-e550-0410-aec6-3dcde31c8c00