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.
container,
      );
      expect(portalContainer.innerHTML).toBe('<div>portal:1</div>');
      expect(container.innerHTML).toBe('<div></div>');
      ReactDOM.render(
        <div>
          {ReactDOM.unstable_createPortal(<div>portal:2</div>, portalContainer)}
        </div>,
        container,
      );
      expect(portalContainer.innerHTML).toBe('<div>portal:2</div>');
      expect(container.innerHTML).toBe('<div></div>');
      ReactDOM.render(
        <div>
          {ReactDOM.unstable_createPortal(<p>portal:3</p>, portalContainer)}
        </div>,
        container,
      );
      expect(portalContainer.innerHTML).toBe('<p>portal:3</p>');
      expect(container.innerHTML).toBe('<div></div>');
      ReactDOM.render(
        <div>
          {ReactDOM.unstable_createPortal(['Hi', 'Bye'], portalContainer)}
        </div>,
        container,
      );
      expect(portalContainer.innerHTML).toBe('HiBye');
      expect(container.innerHTML).toBe('<div></div>');
      ReactDOM.render(
        <div>