bool is_upstream(JSObject *obj) {
  MOZ_ASSERT(is_instance(obj));
  return JS::GetReservedSlot(obj, Slots::IsUpstream).toBoolean();
}
bool is_upstream(JSObject *obj) {
  MOZ_ASSERT(is_instance(obj));
  return JS::GetReservedSlot(obj, Slots::IsUpstream).toBoolean();
}