mash: Port mojo:ash_sysui's ContextMenuMus to mojo:ash.

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index 2c05b0cf0c297498d9c985ed57cb241629e7f4a6..3db0a06101b8f4178ba92b0bbf246f701d6bb07e 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -56,6 +56,7 @@ class ShellObserver;
 class SystemTrayDelegate;
 class SystemTrayNotifier;
 class ToastManager;
+class WallpaperDelegate;
 class WindowCycleController;
 class WindowCycleEventFilter;
 class WindowResizer;
@@ -142,6 +143,8 @@ class ASH_EXPORT WmShell {
 
   ToastManager* toast_manager() { return toast_manager_.get(); }
 
+  WallpaperDelegate* wallpaper_delegate() { return wallpaper_delegate_.get(); }
+
   WindowCycleController* window_cycle_controller() {
     return window_cycle_controller_.get();
   }
@@ -408,6 +411,7 @@ class ASH_EXPORT WmShell {
   std::unique_ptr<SystemTrayNotifier> system_tray_notifier_;
   std::unique_ptr<SystemTrayDelegate> system_tray_delegate_;
   std::unique_ptr<ToastManager> toast_manager_;
+  std::unique_ptr<WallpaperDelegate> wallpaper_delegate_;
   std::unique_ptr<WindowCycleController> window_cycle_controller_;
   std::unique_ptr<WindowSelectorController> window_selector_controller_;