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];
```

emitEvent('onMountRootComponent', debugID);
  },
  onMountComponent(debugID) {
    emitEvent('onMountComponent', debugID);
  },
  onUpdateComponent(debugID) {
    emitEvent('onUpdateComponent', debugID);
  },
  onUnmountComponent(debugID) {
    emitEvent('onUnmountComponent', debugID);
  },
  onTestEvent() {
    emitEvent('onTestEvent');
  },
};
if (__DEV__) {
  var ReactInvalidSetStateWarningDevTool = require('ReactInvalidSetStateWarningDevTool');
  var ReactNativeOperationHistoryDevtool = require('ReactNativeOperationHistoryDevtool');
  var ReactComponentTreeDevtool = require('ReactComponentTreeDevtool');
  ReactDebugTool.addDevtool(ReactInvalidSetStateWarningDevTool);
  ReactDebugTool.addDevtool(ReactComponentTreeDevtool);
  ReactDebugTool.addDevtool(ReactNativeOperationHistoryDevtool);
  var url = (ExecutionEnvironment.canUseDOM && window.location.href) || '';
  if ((/[?&]react_perf\b/).test(url)) {
    ReactDebugTool.beginProfiling();
  }
}
module.exports = ReactDebugTool;