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];
```

);
    invariant(
      container && (
        container.nodeType === ELEMENT_NODE_TYPE ||
        container.nodeType === DOC_NODE_TYPE ||
        container.nodeType === DOCUMENT_FRAGMENT_NODE_TYPE
      ),
      'unmountComponentAtNode(...): Target container is not a DOM element.'
    );
    var prevComponent = getTopLevelWrapperInContainer(container);
    if (!prevComponent) {
      
      
      var containerHasNonRootReactChild = hasNonRootReactChild(container);
      
      var isContainerReactRoot =
        container.nodeType === 1 && container.hasAttribute(ROOT_ATTR_NAME);
      if (__DEV__) {
        warning(
          !containerHasNonRootReactChild,
          'unmountComponentAtNode(): The node you\'re attempting to unmount ' +
          'was rendered by React and is not a top-level container. %s',
          (
            isContainerReactRoot ?
              'You may have accidentally passed in a React root node instead ' +
              'of its container.' :
              'Instead, have the parent component update its state and ' +
              'rerender in order to remove this component.'
          )
        );