* 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
content::RenderFrameHost* rfh) {
  bool handled = true;
  IPC_BEGIN_MESSAGE_MAP_WITH_PARAM(BrowserWindow, message, rfh)
    IPC_MESSAGE_HANDLER(AtomFrameHostMsg_UpdateDraggableRegions,
                        UpdateDraggableRegions)
    IPC_MESSAGE_UNHANDLED(handled = false)
  IPC_END_MESSAGE_MAP()
  return handled;
}
void BrowserWindow::OnCloseContents() {
  DCHECK(web_contents());
  
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  for (v8::Local<v8::Value> value : child_windows_.Values(isolate())) {
    mate::Handle<BrowserWindow> child;
    if (mate::ConvertFromV8(isolate(), value, &child) && !child.IsEmpty())
      child->window()->CloseImmediately();
  }
  
  
  
  
  
  window()->CloseImmediately();
  
  window_unresponsive_closure_.Cancel();
}
void BrowserWindow::OnRendererResponsive() {