Given the following test case

``` jsx
function TestCmp() {
  return <span>{NaN}</span>;
}

ReactDOM.render(<TestCmp />, document.getElementById('app'));
```

Produces the following warning:

```
Warning: Component's children should not be mutated.
    in span (created by TestCmp)
    in TestCmp (created by Unknown)
```

This is probably caused by [this mutation check](https://github.com/facebook/react/blob/328fc75bc910032ff37dc9d93429fb14b476bd0d/src/renderers/shared/hooks/ReactChildrenMutationWarningHook.js#L34), which was introduced in 15.3.0, but it doesn't work for NaN, because NaN != NaN

componentWillMount() {
        this.forceUpdate();
        setTimeout(() => {
          this.forceUpdate();
        });
      }
      render() {
        return <div onClick={() => {}}></div>;
      }
    }
    spyOn(console, 'error');
    ReactServerRendering.renderToString(<Baz />);
    jest.runOnlyPendingTimers();
    expect(console.error.calls.count()).toBe(1);
    expect(console.error.calls.mostRecent().args[0]).toBe(
      'Warning: forceUpdate(...): Can only update a mounting component. ' +
      'This usually means you called forceUpdate() outside componentWillMount() on the server. ' +
      'This is a no-op. Please check the code for the Baz component.'
    );
    var markup = ReactServerRendering.renderToStaticMarkup(<Baz />);
    expect(markup).toBe('<div></div>');
  });
  it('warns when children are mutated before render', () => {
    function normalizeCodeLocInfo(str) {