I was testing latest refactor of PerfTools.
When using printOperations() often (but not always) I get 

```
Uncaught TypeError: Cannot read property 'displayName' of undefined
```

in getOperations() on the line:

```
var {displayName, ownerID} = treeSnapshot[instanceID];
```

var measurements = measure(fn);
    var summary = ReactPerf.getWasted(measurements);
    expect(summary).toEqual([]);
  }
  it('should not count initial render as waste', function() {
    expectNoWaste(() => {
      ReactTestUtils.renderIntoDocument(<App />);
    });
  });
  it('should not count unmount as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div>hello</Div>, container);
    expectNoWaste(() => {
      ReactDOM.unmountComponentAtNode(container);
    });
  });
  it('should not count content update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div>hello</Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div>hello world</Div>, container);