render() {
          return (
            <React.unstable_AsyncMode>
              <Foo>
                <Baz />
              </Foo>
            </React.unstable_AsyncMode>
          );
        }
      }
      class Foo extends React.Component {
        componentWillMount() {}
        render() {
          return this.props.children;
        }
      }
      class Bar extends React.Component {
        componentWillMount() {}
        render() {
          return null;
        }
      }
      class Baz extends React.Component {