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

if (__DEV__) {
    eventHandlers.forEach(function(handler) {
      try {
        if (handler[handlerFunctionName]) {
          handler[handlerFunctionName](arg1, arg2, arg3, arg4, arg5);
        }
      } catch (e) {
        warning(
          handlerDoesThrowForEvent[handlerFunctionName],
          'exception thrown by devtool while handling %s: %s',
          handlerFunctionName,
          e + '\n' + e.stack
        );
        handlerDoesThrowForEvent[handlerFunctionName] = true;
      }
    });
  }
}
var isProfiling = false;
var flushHistory = [];
var currentFlushNesting = 0;
var currentFlushMeasurements = null;
var currentFlushStartTime = null;
var currentTimerDebugID = null;
var currentTimerStartTime = null;
var currentTimerType = null;
function clearHistory() {