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

onUpdateComponent(debugID: DebugID): void {
    checkDebugID(debugID);
    markEnd(debugID, 'update');
    emitEvent('onUpdateComponent', debugID);
  },
  onBeforeUnmountComponent(debugID: DebugID): void {
    checkDebugID(debugID);
    emitEvent('onBeforeUnmountComponent', debugID);
    markBegin(debugID, 'unmount');
  },
  onUnmountComponent(debugID: DebugID): void {
    checkDebugID(debugID);
    markEnd(debugID, 'unmount');
    emitEvent('onUnmountComponent', debugID);
  },
  onTestEvent(): void {
    emitEvent('onTestEvent');
  },
};
(ReactDebugTool: any).addDevtool = ReactDebugTool.addHook;
(ReactDebugTool: any).removeDevtool = ReactDebugTool.removeHook;
ReactDebugTool.addHook(ReactInvalidSetStateWarningHook);
ReactDebugTool.addHook(ReactComponentTreeHook);
ReactDebugTool.addHook(ReactChildrenMutationWarningHook);
var url = (ExecutionEnvironment.canUseDOM && window.location.href) || '';
if ((/[?&]react_perf\b/).test(url)) {
  ReactDebugTool.beginProfiling();
}
module.exports = ReactDebugTool;