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

it('should not count raw HTML update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(
      <Div dangerouslySetInnerHTML={{__html: 'me'}} />,
      container
    );
    expectNoWaste(() => {
      ReactDOM.render(
        <Div dangerouslySetInnerHTML={{__html: 'you'}} />,
        container
      );
    });
  });
  it('should not count child reordering as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div><div key="A" /><div key="B" /></Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div><div key="B" /><div key="A" /></Div>, container);
    });
  });
  it('should not count text update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div>{'hello'}{'world'}</Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div>{'hello'}{'friend'}</Div>, container);
    });
  });
  it('should not count replacing null with a host as waste', function() {
    var element = null;
    function Foo() {