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

return now++;
    });
    if (typeof console.table !== 'function') {
      console.table = () => {};
      console.table.isFake = true;
    }
    React = require('React');
    ReactDOM = require('ReactDOM');
    ReactPerf = require('ReactPerf');
    ReactTestUtils = require('ReactTestUtils');
    emptyFunction = require('emptyFunction');
    App = React.createClass({
      render: function() {
        return <div><Box /><Box flip={this.props.flipSecond} /></div>;
      },
    });
    Box = React.createClass({
      render: function() {
        return <div key={!!this.props.flip}><input /></div>;
      },
    });
    
    Div = React.createClass({
      render: function() {
        return <div {...this.props} />;
      },
    });
    LifeCycle = React.createClass({
      shouldComponentUpdate: emptyFunction.thatReturnsTrue,
      componentWillMount: emptyFunction,