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.
parentInstance: Instance | Container,
    instance: Instance | TextInstance,
  ) {
    if (instance.nodeType === 1) {
      warnForDeletedHydratableElement(parentInstance, (instance: any));
    } else {
      warnForDeletedHydratableText(parentInstance, (instance: any));
    }
  },
  didNotFindHydratableInstance(
    parentInstance: Instance | Container,
    type: string,
    props: Props,
  ) {
    warnForInsertedHydratedElement(parentInstance, type, props);
  },
  didNotFindHydratableTextInstance(
    parentInstance: Instance | Container,
    text: string,
  ) {
    warnForInsertedHydratedText(parentInstance, text);
  },
  scheduleDeferredCallback: ReactDOMFrameScheduling.rIC,
  useSyncScheduling: !ReactDOMFeatureFlags.fiberAsyncScheduling,
});
ReactGenericBatching.injection.injectFiberBatchedUpdates(
  DOMRenderer.batchedUpdates,
);
var warnedAboutHydrateAPI = false;
function renderSubtreeIntoContainer(