### 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
break;
          default:
            break;
        }
      }
      break;
  }
}
void NativeWindowViews::SetForwardMouseMessages(bool forward) {
  if (forward && !forwarding_mouse_messages_) {
    forwarding_mouse_messages_ = true;
    forwarding_windows_.insert(this);
    
    
    SetWindowSubclass(legacy_window_, SubclassProc, 1,
                      reinterpret_cast<DWORD_PTR>(this));
    if (!mouse_hook_) {
      mouse_hook_ = SetWindowsHookEx(WH_MOUSE_LL, MouseHookProc, NULL, 0);
    }
  } else if (!forward && forwarding_mouse_messages_) {
    forwarding_mouse_messages_ = false;
    forwarding_windows_.erase(this);
    RemoveWindowSubclass(legacy_window_, SubclassProc, 1);
    if (forwarding_windows_.size() == 0) {
      UnhookWindowsHookEx(mouse_hook_);
      mouse_hook_ = NULL;
    }
  }
}
LRESULT CALLBACK NativeWindowViews::SubclassProc(HWND hwnd,