Sync wallpaper based on sync themes setting

chrome/common/extensions/api/wallpaper_private.json

Index: chrome/common/extensions/api/wallpaper_private.json
diff --git a/chrome/common/extensions/api/wallpaper_private.json b/chrome/common/extensions/api/wallpaper_private.json
index 23159062a8cbd548e454d4e6e4d87e11531dee7b..7ad50f6c6324951f2f8d4c0687cacfd03c3b23d0 100644
--- a/chrome/common/extensions/api/wallpaper_private.json
+++ b/chrome/common/extensions/api/wallpaper_private.json
@@ -38,6 +38,25 @@
         ]
       },
       {
+        "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",