Make the third party wallpaper syncable through different devices.

chrome/common/extensions/api/wallpaper_private.json

 // Copyright (c) 2012 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.
 
 [
   {
     "namespace":"wallpaperPrivate",
     "compiler_options": {
       "implemented_in": "chrome/browser/chromeos/extensions/wallpaper_private_api.h"
     },
@@ skipping 242 matching lines @@
               }
             ]
           }
         ]
       }
     ],
     "events": [
       {
         "name": "onWallpaperChangedBy3rdParty",
         "type": "function",
-        "description": "This event is sent when the current wallpaper was set by a third party application."
+        "description": "This event is sent when the current wallpaper was set by a third party application.",
+        "parameters": [
+          {
+            "type": "binary",
+            "name": "wallpaper",
+            "description": "The third party custom wallpaper data."
+          },
+          {
+            "type": "binary",
+            "name": "thumbnail",
+            "description": "The third party custom wallpaper thumbnail data."
+          },
+          {
+            "name": "layout",
+            "$ref": "wallpaper.WallpaperLayout"
+          }
+        ]
       }
     ]
   }
 ]