cheets: implement cros side of WallpaperManagerService.

components/arc/set_wallpaper_delegate.h

Index: components/arc/set_wallpaper_delegate.h
diff --git a/components/arc/set_wallpaper_delegate.h b/components/arc/set_wallpaper_delegate.h
index 28e5ed038c5248a219b2b3f78e1294c8d4a7cd5a..9494f5b89987ae988ad7b0050061aeebf6b73b57 100644
--- a/components/arc/set_wallpaper_delegate.h
+++ b/components/arc/set_wallpaper_delegate.h
@@ -12,12 +12,22 @@
 namespace arc {
 
 // Delegate to allow setting the wallpaper.
+// TODO(muyuanli): This class will be removed once ArcIntentHelper migrates to
+// WallpaperManager API.
 class SetWallpaperDelegate {
  public:
   virtual ~SetWallpaperDelegate() = default;
 
+  static SetWallpaperDelegate* instance() { return instance_; }
+  static void set_instance(SetWallpaperDelegate* delegate) {
+    instance_ = delegate;
+  }
+
   // Sets an image represented in JPEG format as the wallpaper.
-  virtual void SetWallpaper(std::vector<uint8_t> jpeg_data) = 0;
+  virtual void SetWallpaperJpeg(const std::vector<uint8_t>& jpeg_data) = 0;
+
+ private:
+  static SetWallpaperDelegate* instance_;
 };
 
 }  // namespace arc