cheets: add wallpaper observer to arc_wallpaper_service.

chrome/browser/chromeos/arc/arc_wallpaper_service.h

Index: chrome/browser/chromeos/arc/arc_wallpaper_service.h
diff --git a/chrome/browser/chromeos/arc/arc_wallpaper_service.h b/chrome/browser/chromeos/arc/arc_wallpaper_service.h
index 4cf806d6b8622e9fd5a467cc9bb0e7f924a56c25..d05d4193921d2eccdc55f1a5b7d796321f7a6158 100644
--- a/chrome/browser/chromeos/arc/arc_wallpaper_service.h
+++ b/chrome/browser/chromeos/arc/arc_wallpaper_service.h
@@ -11,6 +11,7 @@
 #include <set>
 #include <vector>
 
+#include "ash/common/wallpaper/wallpaper_controller_observer.h"
 #include "base/macros.h"
 #include "chrome/browser/image_decoder.h"
 #include "components/arc/arc_service.h"
@@ -25,6 +26,7 @@ namespace arc {
 // Lives on the UI thread.
 class ArcWallpaperService
     : public ArcService,
+      public ash::WallpaperControllerObserver,
       public ImageDecoder::ImageRequest,
       public InstanceHolder<mojom::WallpaperInstance>::Observer,
       public mojom::WallpaperHost {
@@ -45,7 +47,12 @@ class ArcWallpaperService
   void OnImageDecoded(const SkBitmap& bitmap) override;
   void OnDecodeImageFailed() override;
 
+  // WallpaperControllerObserver implementation.
+  void OnWallpaperDataChanged() override;
+
  private:
+  mojom::WallpaperInstance* GetWallpaperInstance(uint32_t min_version);
+
   mojo::Binding<mojom::WallpaperHost> binding_;
   DISALLOW_COPY_AND_ASSIGN(ArcWallpaperService);
 };