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* Electron version: 2.0.0-beta.3
* Operating system: Ubuntu 16.04.04 LTS

### Expected behavior

App menu should be visible

### Actual behavior

App menu is invisible

### How to reproduce

- Run `electron`
- Observe that the app menu is invisible. It is still possible to open submenus.

![screenshot from 2018-03-14 17-01-18](https://user-images.githubusercontent.com/19880051/37415303-7296c25e-27ab-11e8-8284-d213c8bf5230.png)

atom/browser/ui/views/menu_bar.cc
return kViewClassName;
}
void MenuBar::OnMenuButtonClicked(views::MenuButton* source,
                                  const gfx::Point& point,
                                  const ui::Event* event) {
  
  SetAcceleratorVisibility(false);
  if (!menu_model_)
    return;
  if (!window_->IsFocused())
    window_->Focus(true);
  int id = source->tag();
  AtomMenuModel::ItemType type = menu_model_->GetTypeAt(id);
  if (type != AtomMenuModel::TYPE_SUBMENU) {
    menu_model_->ActivatedAt(id, 0);
    return;
  }
  
  MenuDelegate* menu_delegate = new MenuDelegate(this);
  menu_delegate->RunMenu(menu_model_->GetSubmenuModelAt(id), source);
}
void MenuBar::OnNativeThemeChanged(const ui::NativeTheme* theme) {