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

return flushHistory;
  },
  onBeginFlush(): void {
    currentFlushNesting++;
    resetMeasurements();
    pauseCurrentLifeCycleTimer();
    emitEvent('onBeginFlush');
  },
  onEndFlush(): void {
    resetMeasurements();
    currentFlushNesting--;
    resumeCurrentLifeCycleTimer();
    emitEvent('onEndFlush');
  },
  onBeginLifeCycleTimer(debugID: DebugID, timerType: TimerType): void {
    checkDebugID(debugID);
    emitEvent('onBeginLifeCycleTimer', debugID, timerType);
    markBegin(debugID, timerType);
    beginLifeCycleTimer(debugID, timerType);
  },
  onEndLifeCycleTimer(debugID: DebugID, timerType: TimerType): void {
    checkDebugID(debugID);
    endLifeCycleTimer(debugID, timerType);
    markEnd(debugID, timerType);
    emitEvent('onEndLifeCycleTimer', debugID, timerType);
  },
  onBeginProcessingChildContext(): void {
    emitEvent('onBeginProcessingChildContext');
  },
  onEndProcessingChildContext(): void {