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.
if (__DEV__) {
  var lowPriorityWarning = require('lowPriorityWarning');
  var warning = require('fbjs/lib/warning');
  var validateDOMNesting = require('validateDOMNesting');
  var {updatedAncestorInfo} = validateDOMNesting;
  if (
    typeof Map !== 'function' ||
    Map.prototype == null ||
    typeof Map.prototype.forEach !== 'function' ||
    typeof Set !== 'function' ||
    Set.prototype == null ||
    typeof Set.prototype.clear !== 'function' ||
    typeof Set.prototype.forEach !== 'function'
  ) {
    warning(
      false,
      'React depends on Map and Set built-in types. Make sure that you load a ' +
        'polyfill in older browsers. http://fb.me/react-polyfills',
    );
  }
}
require('ReactDOMClientInjection');
require('ReactDOMInjection');
ReactControlledComponent.injection.injectFiberControlledHostComponent(
  ReactDOMFiberComponent,
);
findDOMNode._injectFiber(function(fiber: Fiber) {
  return DOMRenderer.findHostInstance(fiber);
});
type DOMContainer =