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>
 #include <set>
 #include <vector>
 
 #include "base/macros.h"
 #include "chrome/browser/image_decoder.h"
 #include "components/arc/set_wallpaper_delegate.h"
 
 class SkBitmap;
 
 namespace arc {
 
 // Lives on the UI thread.
 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);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_