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 stubNode;
    beforeEach(function() {
      stubNode = document.createElement('div');
      ReactDOMComponentTree.precacheNode({}, stubNode);
    });
    it('should set values as properties by default', function() {
      DOMPropertyOperations.setValueForProperty(stubNode, 'title', 'Tip!');
      expect(stubNode.title).toBe('Tip!');
    });
    it('should set values as attributes if necessary', function() {
      DOMPropertyOperations.setValueForProperty(stubNode, 'role', '#');
      expect(stubNode.getAttribute('role')).toBe('#');
      expect(stubNode.role).toBeUndefined();
    });
    it('should set values as namespace attributes if necessary', function() {
      spyOn(stubNode, 'setAttributeNS');
      DOMPropertyOperations.setValueForProperty(
        stubNode,
        'xlinkHref',
        'about:blank'
      );
      expect(stubNode.setAttributeNS.argsForCall.length).toBe(1);
      expect(stubNode.setAttributeNS.argsForCall[0])
        .toEqual(['http://www.w3.org/1999/xlink', 'xlink:href', 'about:blank']);
    });
    it('should set values as boolean properties', function() {
      DOMPropertyOperations.setValueForProperty(stubNode, 'disabled', 'disabled');
      expect(stubNode.getAttribute('disabled')).toBe('');
      DOMPropertyOperations.setValueForProperty(stubNode, 'disabled', true);
      expect(stubNode.getAttribute('disabled')).toBe('');