Currently if React is not loaded, ReactDOM shows this:

<img width="664" alt="screen shot 2017-08-08 at 3 36 52 pm" src="https://user-images.githubusercontent.com/810438/29077217-784c7624-7c4f-11e7-88bc-b055407523a9.png">

We should throw a nicer error message in the entry point I think.
'with ReactDOM.hydrate() if you want React to attach to the server HTML.',
        );
      }
    }
    const newRoot = DOMRenderer.createContainer(container);
    root = container._reactRootContainer = newRoot;
    
    DOMRenderer.unbatchedUpdates(() => {
      DOMRenderer.updateContainer(children, newRoot, parentComponent, callback);
    });
  } else {
    DOMRenderer.updateContainer(children, root, parentComponent, callback);
  }
  return DOMRenderer.getPublicRootInstance(root);
}
var ReactDOMFiber = {
  hydrate(
    element: ReactElement<any>,
    container: DOMContainer,
    callback: ?Function,
  ) {
    
    return renderSubtreeIntoContainer(null, element, container, true, callback);
  },
  render(
    element: ReactElement<any>,
    container: DOMContainer,
    callback: ?Function,
  ) {
    if (ReactFeatureFlags.disableNewFiberFeatures) {