cheets: implement cros side of WallpaperManagerService.

chrome/browser/chromeos/arc/arc_wallpaper_handler.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 10 matching lines @@
 
 // Lives on the UI thread.
 class ArcWallpaperHandler : public SetWallpaperDelegate,
                             public ImageDecoder::ImageRequest {
  public:
   ArcWallpaperHandler();
   ~ArcWallpaperHandler() override;
 
   // SetWallpaperDelegate implementation.
   void SetWallpaper(std::vector<uint8_t> jpeg_data) override;
-
+  // Returns current wallpaper.
+  void GetWallpaper(const base::Callback<void(std::vector<uint8_t> image)>&
+                        callback) const override;
   // ImageDecoder::ImageRequest implementation.
   void OnImageDecoded(const SkBitmap& bitmap) override;
   void OnDecodeImageFailed() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ArcWallpaperHandler);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_