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

render() {
        var inner = <Wrapper object={innerObj} ref={(c) => this.innerRef = c} />;
        var outer = (
          <Wrapper object={outerObj} ref={(c) => this.outerRef = c}>
            {inner}
          </Wrapper>
        );
        return outer;
      }
      componentDidMount() {
        expect(this.innerRef.getObject()).toEqual(innerObj);
        expect(this.outerRef.getObject()).toEqual(outerObj);
        mounted = true;
      }
    }
    var instance = <Component />;
    instance = ReactTestUtils.renderIntoDocument(instance);
    expect(mounted).toBe(true);
  });
  it('should support new-style refs with mixed-up owners', () => {
    class Wrapper extends React.Component {
      getTitle = () => {
        return this.props.title;
      };
      render() {
        return this.props.getContent();
      }
    }
    var mounted = false;
    class Component extends React.Component {