cheets: implement cros side of WallpaperManagerService.

chrome/browser/chromeos/arc/arc_wallpaper_handler.h

Index: chrome/browser/chromeos/arc/arc_wallpaper_handler.h
diff --git a/chrome/browser/chromeos/arc/arc_wallpaper_handler.h b/chrome/browser/chromeos/arc/arc_wallpaper_handler.h
index 3b0b132fcbd722353d935f0d9a09a6814d58b43e..bc708c176185742d11a0208f12e4988b9142edaf 100644
--- a/chrome/browser/chromeos/arc/arc_wallpaper_handler.h
+++ b/chrome/browser/chromeos/arc/arc_wallpaper_handler.h
@@ -23,17 +23,19 @@ namespace arc {
 class ArcWallpaperHandler : public SetWallpaperDelegate,
                             public ImageDecoder::ImageRequest {
  public:
-  ArcWallpaperHandler();
   ~ArcWallpaperHandler() override;
 
+  static std::shared_ptr<ArcWallpaperHandler> Get();
   // SetWallpaperDelegate implementation.
   void SetWallpaper(std::vector<uint8_t> jpeg_data) override;
-
+  // Returns current wallpaper.
+  std::vector<uint8_t> GetWallpaper() const override;
   // ImageDecoder::ImageRequest implementation.
   void OnImageDecoded(const SkBitmap& bitmap) override;
   void OnDecodeImageFailed() override;
 
  private:
+  ArcWallpaperHandler();
   DISALLOW_COPY_AND_ASSIGN(ArcWallpaperHandler);
 };