Hello,

After updating to React 15.0.1, we are getting the following error:

```
Uncaught TypeError: Cannot read property 'addEventListener' of null
```

![image](https://cloud.githubusercontent.com/assets/4996164/14602577/5bb4e9f2-0571-11e6-9aa1-98de49f50d76.png)

var aUpdated = false;
    var A = React.createClass({
      getInitialState: function() {
        return {x: 0};
      },
      componentDidUpdate: function() {
        expect(ReactDOM.findDOMNode(b).textContent).toBe('B1');
        aUpdated = true;
      },
      render: function() {
        return <div>A{this.state.x}</div>;
      },
    });
    var B = React.createClass({
      getInitialState: function() {
        return {x: 0};
      },
      render: function() {
        return <div>B{this.state.x}</div>;
      },
    });
    a = ReactTestUtils.renderIntoDocument(<A />);
    b = ReactTestUtils.renderIntoDocument(<B />);
    ReactUpdates.batchedUpdates(function() {
      a.setState({x: 1});
      b.setState({x: 1});
    });
    expect(aUpdated).toBe(true);
  });
  it('should flush updates in the correct order', function() {