### 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.cc
const gfx::Rect& bounds) const {
  if (!has_frame())
    return bounds;
  gfx::Rect content_bounds(bounds);
#if defined(OS_WIN)
  HWND hwnd = GetAcceleratedWidget();
  content_bounds.set_size(DIPToScreenRect(hwnd, content_bounds).size());
  RECT rect;
  SetRectEmpty(&rect);
  DWORD style = ::GetWindowLong(hwnd, GWL_STYLE);
  DWORD ex_style = ::GetWindowLong(hwnd, GWL_EXSTYLE);
  AdjustWindowRectEx(&rect, style, FALSE, ex_style);
  content_bounds.set_width(content_bounds.width() - (rect.right - rect.left));
  content_bounds.set_height(content_bounds.height() - (rect.bottom - rect.top));
  content_bounds.set_size(ScreenToDIPRect(hwnd, content_bounds).size());
#endif
  if (root_view_->HasMenu() && root_view_->IsMenuBarVisible()) {
    int menu_bar_height = root_view_->GetMenuBarHeight();
    content_bounds.set_y(content_bounds.y() + menu_bar_height);
    content_bounds.set_height(content_bounds.height() - menu_bar_height);
  }
  return content_bounds;
}
void NativeWindowViews::UpdateDraggableRegions(
    std::unique_ptr<SkRegion> region) {
  draggable_region_ = std::move(region);
}
#if defined(OS_WIN)
void NativeWindowViews::SetIcon(HICON window_icon, HICON app_icon) {