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

ash/sysui/shell_delegate_mus.h

Index: ash/sysui/shell_delegate_mus.h
diff --git a/ash/sysui/shell_delegate_mus.h b/ash/sysui/shell_delegate_mus.h
index 4a497ee9b7b01b9decc6411fb222e6f29171ca6d..0c6a81b8828561f3e2a61a0cffa3508d8700bd37 100644
--- a/ash/sysui/shell_delegate_mus.h
+++ b/ash/sysui/shell_delegate_mus.h
@@ -39,7 +39,7 @@ class ShellDelegateMus : public ShellDelegate {
   app_list::AppListPresenter* GetAppListPresenter() override;
   ShelfDelegate* CreateShelfDelegate(ShelfModel* model) override;
   SystemTrayDelegate* CreateSystemTrayDelegate() override;
-  UserWallpaperDelegate* CreateUserWallpaperDelegate() override;
+  WallpaperDelegate* CreateWallpaperDelegate() override;
   SessionStateDelegate* CreateSessionStateDelegate() override;
   AccessibilityDelegate* CreateAccessibilityDelegate() override;
   NewWindowDelegate* CreateNewWindowDelegate() override;