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)

ReactDOM.render(<Div><span /></Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div><span /><span /></Div>, container);
    });
  });
  it('should not count child removal as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div><span /><span /></Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div><span /></Div>, container);
    });
  });
  it('should not count property update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div className="yellow">hey</Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div className="blue">hey</Div>, container);
    });
  });
  it('should not count style update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div style={{color: 'yellow'}}>hey</Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div style={{color: 'blue'}}>hey</Div>, container);
    });
  });
  it('should not count property removal as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div className="yellow">hey</Div>, container);
    expectNoWaste(() => {