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 (Array.isArray(childNode)) {
    var closingComment = childNode[1];
    childNode = childNode[0];
    removeDelimitedText(parentNode, childNode, closingComment);
    parentNode.removeChild(closingComment);
  }
  parentNode.removeChild(childNode);
}
function moveDelimitedText(
  parentNode,
  openingComment,
  closingComment,
  referenceNode
) {
  var node = openingComment;
  while (true) {
    var nextNode = node.nextSibling;
    insertChildAt(parentNode, node, referenceNode);
    if (node === closingComment) {
      break;
    }
    node = nextNode;
  }
}
function removeDelimitedText(parentNode, startNode, closingComment) {