chromeos: Move device shutdown handling out of chrome into ash

ash/mus/manifest.json

 {
   "name": "service:ash",
   "display_name": "Ash Window Manager and Shell",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "ash": [
           "ash::mojom::LocaleNotificationController",
           "ash::mojom::ShelfController",
+          "ash::mojom::ShutdownController",
           "ash::mojom::SystemTray",
           "ash::mojom::WallpaperController"
         ],
         "mus:window_manager": [ "ui::mojom::AcceleratorRegistrar" ]
       },
       "requires": {
         "*": [ "accessibility", "app" ],
         "service:content_browser": [ "ash" ],
         "service:mash_session": [ "mash_session:session" ],
         "service:ui": [ "ui:window_manager" ],
         "service:touch_hud": [ "mash:launchable" ]
       }
     }
   }
 }