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

var summary = ReactPerf.getWasted(measurements);
    expect(summary).toEqual([{
      key: 'App',
      instanceCount: 1,
      inclusiveRenderDuration: 3,
      renderCount: 1,
    }, {
      key: 'App > Box',
      instanceCount: 2,
      inclusiveRenderDuration: 2,
      renderCount: 2,
    }]);
  });
  it('should count no-op update in child as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<App />, container);
    
    
    var measurements = measure(() => {
      ReactDOM.render(<App flipSecond={true} />, container);
    });
    var summary = ReactPerf.getWasted(measurements);
    expect(summary).toEqual([{
      key: 'App > Box',
      instanceCount: 1,
      inclusiveRenderDuration: 1,
      renderCount: 1,
    }]);
  });
  function expectNoWaste(fn) {