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 property removal as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div className="yellow">hey</Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div>hey</Div>, container);
    });
  });
  it('should not count raw HTML update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(
      <Div dangerouslySetInnerHTML={{__html: 'me'}} />,
      container
    );
    expectNoWaste(() => {
      ReactDOM.render(
        <Div dangerouslySetInnerHTML={{__html: 'you'}} />,
        container
      );
    });
  });
  it('should not count child reordering as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div><div key="A" /><div key="B" /></Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div><div key="B" /><div key="A" /></Div>, container);
    });
  });
  it('should not count text update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div>{'hello'}{'world'}</Div>, container);