void set_url(JSObject *obj, Value url) {
  MOZ_ASSERT(is_instance(obj));
  MOZ_ASSERT(url.isString());
  JS::SetReservedSlot(obj, Slots::URL, url);
}
void set_url(JSObject *obj, Value url) {
  MOZ_ASSERT(is_instance(obj));
  MOZ_ASSERT(url.isString());
  JS::SetReservedSlot(obj, Slots::URL, url);
}