Sync wallpaper based on sync themes setting

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 20 matching lines @@
               {
                 "name": "result",
                 "type": "object",
                 "additionalProperties": {"type": "any"}
               }
             ]
           }
         ]
       },
       {
+        "name": "getSyncSetting",
+        "type": "function",
+        "description": "Gets the sync themes(and wallpaper on ChromeOS) setting value.",
+        "nodoc": "true",
+        "parameters": [
+          {
+            "type": "function",
+            "name": "callback",
+            "parameters": [
+              {
+                "name": "result",
+                "type": "object",
+                "additionalProperties": {"type": "any"}
+              }
+            ]
+          }
+        ]
+      },
+      {
         "name": "setWallpaperIfExists",
         "type": "function",
         "description": "Sets wallpaper if it exists in the local file system with specified layout",
         "nodoc": "true",
         "parameters": [
           {
             "type": "string",
             "name": "url"
           },
           {
@@ skipping 183 matching lines @@
                 "name": "results",
                 "items": {"type": "string"}
               }
             ]
           }
         ]
       }
     ]
   }
 ]