Calling `ReactDefaultPerf.printWasted()` results in:

```
Uncaught TypeError: Cannot read property 'forEach' of undefined
writes.(anonymous function).forEach @ ReactDefaultPerfAnalysis.js:195
Object.keys.forEach @ ReactDefaultPerfAnalysis.js:192
getUnchangedComponents @ ReactDefaultPerfAnalysis.js:191
getInclusiveSummary @ ReactDefaultPerfAnalysis.js:139
ReactDefaultPerf.getMeasurementsSummaryMap @ ReactDefaultPerf.js:118
ReactDefaultPerf.printWasted @ ReactDefaultPerf.js:133
```

(this is on a page internally at Facebook so I assume it's a fairly recent React version)

/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @emails react-core
 */
'use strict';
describe('ReactDefaultPerf', function() {
  var React;
  var ReactDOM;
  var ReactDOMFeatureFlags;
  var ReactDefaultPerf;
  var ReactTestUtils;
  var ReactDefaultPerfAnalysis;
  var App;
  var Box;
  var Div;
  beforeEach(function() {
    var now = 0;
    jest.setMock('fbjs/lib/performanceNow', function() {
      return now++;
    });
    if (typeof console.table !== 'function') {
      console.table = () => {};
      console.table.isFake = true;