<S> &root,                   typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy) {     ptr = reinterpret_cast<const T *>(root.address()); }  template <typename T> inline MutableHandle<T>::MutableHandle(Rooted<T> *root) {     static_assert(sizeof(MutableHandle<T>) == sizeof(T *),                   "MutableHandle must be binary compatible with T*.");     ptr = root->address(); }  template <typename T> inline MutableHandle<T>::MutableHandle(