ObjectHashTable's key and WeakHashTable's key types are now Handle<Object> instead of Object*.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/257853003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20982 ce2b1a6d-e550-0410-aec6-3dcde31c8c00