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];
```

scryRenderedDOMComponentsWithClass: function(root, classNames) {
    return ReactTestUtils.findAllInRenderedTree(root, function(inst) {
      if (ReactTestUtils.isDOMComponent(inst)) {
        var className = inst.className;
        if (typeof className !== 'string') {
          
          className = inst.getAttribute('class') || '';
        }
        var classList = className.split(/\s+/);
        if (!Array.isArray(classNames)) {
          invariant(
            classNames !== undefined,
            'TestUtils.scryRenderedDOMComponentsWithClass expects a ' +
            'className as a second argument.'
          );
          classNames = classNames.split(/\s+/);
        }
        return classNames.every(function(name) {
          return classList.indexOf(name) !== -1;
        });
      }
      return false;
    });
  },
  /**
   * Like scryRenderedDOMComponentsWithClass 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.
   */