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];
```

});
  });
  it('should not count child addition as waste', function() {
    var container = document.createElement('div');
    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);
    });
  });