* 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.cc
window_unresponsive_closure_.Cancel();
  Emit("responsive");
}
void BrowserWindow::RequestPreferredWidth(int* width) {
  *width = web_contents()->GetPreferredSize().width();
}
void BrowserWindow::OnCloseButtonClicked(bool* prevent_default) {
  
  
  
  *prevent_default = true;
  
  
  
  
  if (window_unresponsive_closure_.IsCancelled())
    ScheduleUnresponsiveEvent(5000);
  if (!web_contents())
    
    return;
  if (web_contents()->NeedToFireBeforeUnload())
    web_contents()->DispatchBeforeUnload();
  else
    web_contents()->Close();
}
void BrowserWindow::OnWindowClosed() {