### Preflight Checklist
* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  * 6.0.0-beta.3
* **Operating System:**
  * Windows 10 (1809)
* **Last Known Working Electron version:**:
  * 5.0.1

### Expected Behavior
Dragging your mouse to the bottom of the screen with a maximized frameless window and a hidden Windows taskbar should make the taskbar appear.

### Actual Behavior
The taskbar does not appear.

### To Reproduce

* Ensure you have Taskbar hiding enabled
![image](https://user-images.githubusercontent.com/144914/57793291-d12d9000-76f5-11e9-8c63-178e928a5358.png)

```sh
$ git clone https://github.com/adill/electron-quick-start -b no-taskbar-unhide
$ npm install
$ npm start || electron .
```

* Move your mouse to the bottom of the screen

### Screenshots

### Additional Information

atom/browser/native_window_views_win.cc
UINT msg,
                                                 WPARAM w_param,
                                                 LPARAM l_param,
                                                 UINT_PTR subclass_id,
                                                 DWORD_PTR ref_data) {
  NativeWindowViews* window = reinterpret_cast<NativeWindowViews*>(ref_data);
  switch (msg) {
    case WM_MOUSELEAVE: {
      
      
      
      
      
      
      
      
      
      
      if (window->forwarding_mouse_messages_) {
        return 0;
      }
      break;
    }
  }
  return DefSubclassProc(hwnd, msg, w_param, l_param);
}
LRESULT CALLBACK NativeWindowViews::MouseHookProc(int n_code,