cheets: implement cros side of WallpaperManagerService.

components/arc/set_wallpaper_delegate.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 COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_
 #define COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_
 
 #include <stdint.h>
 
 #include <vector>
 
 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* GetInstance() { return instance_; }

[Luis Héctor Chávez, 2016/09/08 19:14:24]

nit: Chromium style guide prefers having these inline functions use lowercase
snake_case names.

instance() { return instance_; }
set_instance(SetWallpaperDelegate* instance) { instance_ = instance; }

[Muyuan, 2016/09/08 21:05:25]

Done.

+  static void SetSetWallpaperDelegate(SetWallpaperDelegate* instance) {
+    instance_ = instance;
+  }
+
   // 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
 
 #endif  // COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_