UI: Prevent race condition during emulator startup.

src/xenia/ui/menu_item.h

@@ -19,6 +19,8 @@
 namespace xe {
 namespace ui {
 
+class Window;
+
 class MenuItem {
  public:
   typedef std::unique_ptr<MenuItem, void (*)(MenuItem*)> MenuItemPtr;
@@ -51,6 +53,9 @@ class MenuItem {
   void RemoveChild(MenuItem* child_item);
   MenuItem* child(size_t index);
 
+  virtual void EnableMenuItem(Window& window) = 0;
+  virtual void DisableMenuItem(Window& window) = 0;
+
  protected:
   MenuItem(Type type, const std::wstring& text, const std::wstring& hotkey,
            std::function<void()> callback);