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

key: 'Foo',
      instanceCount: 1,
      totalDuration: 1,
      counts: {
        render: 1,
      },
      durations: {
        render: 1,
      },
    }]);
  });
  it('warns once when using getMeasurementsSummaryMap', function() {
    var measurements = measure(() => {});
    spyOn(console, 'error');
    ReactPerf.getMeasurementsSummaryMap(measurements);
    expect(console.error.calls.length).toBe(1);
    expect(console.error.argsForCall[0][0]).toContain(
      '`ReactPerf.getMeasurementsSummaryMap(...)` is deprecated. Use ' +
      '`ReactPerf.getWasted(...)` instead.'
    );
    ReactPerf.getMeasurementsSummaryMap(measurements);
    expect(console.error.calls.length).toBe(1);
  });
  it('warns once when using printDOM', function() {
    var measurements = measure(() => {});
    spyOn(console, 'error');
    ReactPerf.printDOM(measurements);
    expect(console.error.calls.length).toBe(1);
    expect(console.error.argsForCall[0][0]).toContain(
      '`ReactPerf.printDOM(...)` is deprecated. Use ' +