Given the following test case

``` jsx
function TestCmp() {
  return <span>{NaN}</span>;
}

ReactDOM.render(<TestCmp />, document.getElementById('app'));
```

Produces the following warning:

```
Warning: Component's children should not be mutated.
    in span (created by TestCmp)
    in TestCmp (created by Unknown)
```

This is probably caused by [this mutation check](https://github.com/facebook/react/blob/328fc75bc910032ff37dc9d93429fb14b476bd0d/src/renderers/shared/hooks/ReactChildrenMutationWarningHook.js#L34), which was introduced in 15.3.0, but it doesn't work for NaN, because NaN != NaN

var currentTimer = {
    startTime: currentTimerStartTime,
    nestedFlushStartTime: performanceNow(),
    debugID: currentTimerDebugID,
    timerType: currentTimerType,
  };
  lifeCycleTimerStack.push(currentTimer);
  currentTimerStartTime = 0;
  currentTimerNestedFlushDuration = 0;
  currentTimerDebugID = null;
  currentTimerType = null;
}
function resumeCurrentLifeCycleTimer() {