bug

Warning displayed in console about internal error of React performance measurement code.

``` js
import React from 'react';
import { render } from 'react-dom';
import Perf from 'react-addons-perf';
import { browserHistory, Router } from 'react-router';

import routes from './routes';
import persist from 'altFlux/persist';

persist('docs');

const target = document.getElementById('app');

Perf.start();

render(
  <Router
    routes={routes}
    history={browserHistory}
  />,
  target,
  () => {
    Perf.stop();
    Perf.printWasted();
  }
);
```

![screen shot 2016-05-23 at 9 21 08 am](https://cloud.githubusercontent.com/assets/91464/15472297/5e440d48-20c8-11e6-99d7-363f6d1bdcce.png)

15.1.0
Google Chrome

componentWillMount: 1,
        componentDidMount: 1,
        componentWillReceiveProps: 1,
        componentWillUpdate: 2,
        componentDidUpdate: 2,
        componentWillUnmount: 1,
        render: 3,
      },
      durations: {
        ctor: 1,
        shouldComponentUpdate: 2,
        componentWillMount: 1,
        componentDidMount: 1,
        componentWillReceiveProps: 1,
        componentWillUpdate: 2,
        componentDidUpdate: 2,
        componentWillUnmount: 1,
        render: 3,
      },
    }]);
  });
  it('should include render time of functional components', function() {
    function Foo() {
      return null;
    }
    var container = document.createElement('div');
    var measurements = measure(() => {
      ReactDOM.render(<Foo />, container);
    });
    expect(ReactPerf.getExclusive(measurements)).toEqual([{