cheets: implement cros side of WallpaperManagerService.

components/arc/arc_bridge_service.h

Index: components/arc/arc_bridge_service.h
diff --git a/components/arc/arc_bridge_service.h b/components/arc/arc_bridge_service.h
index 4d1eb4d1ec0405f1a0911c1a754dc1f133ce0ab3..e3883583532af44e4477a62495445074122d351e 100644
--- a/components/arc/arc_bridge_service.h
+++ b/components/arc/arc_bridge_service.h
@@ -120,6 +120,7 @@ class ArcBridgeService {
   }
   InstanceHolder<mojom::TtsInstance>* tts() { return &tts_; }
   InstanceHolder<mojom::VideoInstance>* video() { return &video_; }
+  InstanceHolder<mojom::WallpaperInstance>* wallpaper() { return &wallpaper_; }
 
   // Gets if ARC is currently running.
   bool ready() const { return state() == State::READY; }
@@ -188,6 +189,7 @@ class ArcBridgeService {
   InstanceHolder<mojom::StorageManagerInstance> storage_manager_;
   InstanceHolder<mojom::TtsInstance> tts_;
   InstanceHolder<mojom::VideoInstance> video_;
+  InstanceHolder<mojom::WallpaperInstance> wallpaper_;
 
   // Gets the current state of the bridge service.
   State state() const { return state_; }