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

ReactComponentTreeDevtool.purgeUnmountedComponents();
  ReactHostOperationHistoryDevtool.clearHistory();
}
function getTreeSnapshot(registeredIDs) {
  return registeredIDs.reduce((tree, id) => {
    var ownerID = ReactComponentTreeDevtool.getOwnerID(id);
    var parentID = ReactComponentTreeDevtool.getParentID(id);
    tree[id] = {
      displayName: ReactComponentTreeDevtool.getDisplayName(id),
      text: ReactComponentTreeDevtool.getText(id),
      updateCount: ReactComponentTreeDevtool.getUpdateCount(id),
      childIDs: ReactComponentTreeDevtool.getChildIDs(id),
      
      ownerID: ownerID || ReactComponentTreeDevtool.getOwnerID(parentID),
      parentID,
    };
    return tree;
  }, {});
}
function resetMeasurements() {