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.
portalContainer3,
              ),
              <div key="e">portal1[1]</div>,
            ],
            portalContainer1,
          ),
          <div key="f">normal[1]</div>,
        ],
        container,
      );
      expect(portalContainer1.innerHTML).toBe(
        '<div>portal1[0]</div><div>portal1[1]</div>',
      );
      expect(portalContainer2.innerHTML).toBe('<div>portal2[0]</div>');
      expect(portalContainer3.innerHTML).toBe('<div>portal3[0]</div>');
      expect(container.innerHTML).toBe(
        '<div>normal[0]</div><div>normal[1]</div>',
      );
      ReactDOM.unmountComponentAtNode(container);
      expect(portalContainer1.innerHTML).toBe('');
      expect(portalContainer2.innerHTML).toBe('');
      expect(portalContainer3.innerHTML).toBe('');
      expect(container.innerHTML).toBe('');
    });
    it('should reconcile portal children', () => {
      var portalContainer = document.createElement('div');
      ReactDOM.render(
        <div>
          {ReactDOM.unstable_createPortal(<div>portal:1</div>, portalContainer)}
        </div>,