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..5405822908ce7f36f5f5fad47b549da2dd10270c 100644
--- a/components/arc/set_wallpaper_delegate.h
+++ b/components/arc/set_wallpaper_delegate.h
@@ -6,9 +6,10 @@
 #define COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_
 
 #include <stdint.h>
-
 #include <vector>
 
+#include "base/callback_forward.h"
+
 namespace arc {
 
 // Delegate to allow setting the wallpaper.
@@ -18,6 +19,10 @@ class SetWallpaperDelegate {
 
   // Sets an image represented in JPEG format as the wallpaper.
   virtual void SetWallpaper(std::vector<uint8_t> jpeg_data) = 0;
+  // Gets current wallpaper encoded in JPEG format.
+  virtual void GetWallpaper(
+      const base::Callback<void(std::vector<uint8_t> image)>& callback)
+      const = 0;
 };
 
 }  // namespace arc