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 (!container) {
    return null;
  }
  if (container.nodeType === DOCUMENT_NODE) {
    return container.documentElement;
  } else {
    return container.firstChild;
  }
}
function shouldHydrateDueToLegacyHeuristic(container) {
  const rootElement = getReactRootElementInContainer(container);
  return !!(rootElement &&
    rootElement.nodeType === ELEMENT_NODE &&
    rootElement.hasAttribute(ROOT_ATTRIBUTE_NAME));
}
function shouldAutoFocusHostComponent(type: string, props: Props): boolean {
  switch (type) {
    case 'button':
    case 'input':
    case 'select':
    case 'textarea':
      return !!props.autoFocus;
  }
  return false;
}
var DOMRenderer = ReactFiberReconciler({
  getRootHostContext(rootContainerInstance: Container): HostContext {
    let type;
    let namespace;