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];
```

findRenderedDOMComponentWithClass: function(root, className) {
    var all =
      ReactTestUtils.scryRenderedDOMComponentsWithClass(root, className);
    if (all.length !== 1) {
      throw new Error(
        'Did not find exactly one match (found: ' + all.length + ') ' +
        'for class:' + className
      );
    }
    return all[0];
  },
  /**
   * Finds all instance of components in the rendered tree that are DOM
   * components with the tag name matching `tagName`.
   * @return {array} an array of all the matches.
   */
  scryRenderedDOMComponentsWithTag: function(root, tagName) {
    return ReactTestUtils.findAllInRenderedTree(root, function(inst) {
      return ReactTestUtils.isDOMComponent(inst) &&
            inst.tagName.toUpperCase() === tagName.toUpperCase();
    });
  },
  /**
   * Like scryRenderedDOMComponentsWithTag but expects there to be one result,
   * and returns that one result, or throws exception if there is any other
   * number of matches besides one.
   * @return {!ReactDOMComponent} The one match.
   */
  findRenderedDOMComponentWithTag: function(root, tagName) {
    var all = ReactTestUtils.scryRenderedDOMComponentsWithTag(root, tagName);