* Electron version: 2.0.0-beta.7
* Operating system: macOS 10.13.4

### Expected behavior

<!-- What do you think should happen? -->
When HTML fullscreen mode is active, exiting fullscreen on the window level (clicking the green button or calling `win.setFullScreen(false)` should also exit HTML fullscreen mode.

### Actual behavior

HTML fullscreen mode stays active. Chrome correctly exits HTML fullscreen mode.

### How to reproduce

Use console in the default_app:

```
document.addEventListener('webkitfullscreenchange', () => console.log('webkitfullscreenchange'));
document.documentElement.webkitRequestFullscreen();
```

now exit fullscreen by clicking the green button or run `require('electron').remote.getCurrentWindow().setFullScreen(false);`

Compare to what happens when you do the same in Chrome/Chromium
`webkitfullscreenchange` should be logged twice (once for enter, once for exit)
`document.webkitFullscreenElement` should also be `null`

Possible workaround is:
```
win.on('leave-full-screen', () => {
  win.webContents.executeJavaScript('document.webkitExitFullscreen();');
});
```

atom/browser/api/atom_api_browser_window.h
v8::Local<v8::Value> GetWebContents(v8::Isolate* isolate);
 private:
  
  
  void UpdateDraggableRegions(content::RenderFrameHost* rfh,
                              const std::vector<DraggableRegion>& regions);
  
  std::unique_ptr<SkRegion> DraggableRegionsToSkRegion(
      const std::vector<DraggableRegion>& regions);
  
  void ScheduleUnresponsiveEvent(int ms);
  
  void NotifyWindowUnresponsive();
  
  void Cleanup();
  
  
  base::CancelableClosure window_unresponsive_closure_;
#if defined(OS_MACOSX)
  std::vector<DraggableRegion> draggable_regions_;
#endif
  v8::Global<v8::Value> web_contents_;
  api::WebContents* api_web_contents_;
  base::WeakPtrFactory<BrowserWindow> weak_factory_;
  DISALLOW_COPY_AND_ASSIGN(BrowserWindow);
};
}  
}  
#endif