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 (__DEV__) {
      if (!isProfiling) {
        return;
      }
      isProfiling = false;
      resetMeasurements();
    }
  },
  getFlushHistory() {
    if (__DEV__) {
      return flushHistory;
    }
  },
  onBeginFlush() {
    if (__DEV__) {
      currentFlushNesting++;
      resetMeasurements();
    }
    emitEvent('onBeginFlush');
  },
  onEndFlush() {