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];
```

);
    if (all.length !== 1) {
      throw new Error(
        'Did not find exactly one match (found: ' + all.length + ') ' +
        'for componentType:' + componentType
      );
    }
    return all[0];
  },
  /**
   * Pass a mocked component module to this method to augment it with
   * useful methods that allow it to be used as a dummy React component.
   * Instead of rendering as usual, the component will become a simple
   * <div> containing any provided children.
   *
   * @param {object} module the mock function object exported from a
   *                        module that defines the component to be mocked
   * @param {?string} mockTagName optional dummy root tag name to return
   *                              from render method (overrides
   *                              module.mockTagName if provided)
   * @return {object} the ReactTestUtils object (for chaining)
   */
  mockComponent: function(module, mockTagName) {
    mockTagName = mockTagName || module.mockTagName || 'div';
    module.prototype.render.mockImplementation(function() {
      return React.createElement(
        mockTagName,
        null,
        this.props.children
      );