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 summary = ReactPerf.getWasted(measurements);
    expect(summary).toEqual([{
      key: 'App',
      instanceCount: 1,
      inclusiveRenderDuration: 3,
      renderCount: 1,
    }, {
      key: 'App > Box',
      instanceCount: 2,
      inclusiveRenderDuration: 2,
      renderCount: 2,
    }]);
  });
  it('should count no-op update in child as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<App />, container);
    
    
    var measurements = measure(() => {
      ReactDOM.render(<App flipSecond={true} />, container);
    });
    var summary = ReactPerf.getWasted(measurements);
    expect(summary).toEqual([{
      key: 'App > Box',
      instanceCount: 1,
      inclusiveRenderDuration: 1,
      renderCount: 1,
    }]);
  });
  function expectNoWaste(fn) {