Enable Null Syncable ID which is different than Root ID.

sync/syncable/nigori_util.cc

 // Copyright 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.
 
 #include "sync/syncable/nigori_util.h"
 
 #include <queue>
 #include <string>
 #include <vector>
 
@@ skipping 94 matching lines @@
     NOTREACHED();
     return false;
   }
 
   std::queue<Id> to_visit;
   Id id_string = type_root.GetFirstChildId();
   to_visit.push(id_string);
   while (!to_visit.empty()) {
     id_string = to_visit.front();
     to_visit.pop();
-    if (id_string.IsRoot())
+    if (id_string.IsNull())
       continue;
 
     Entry child(trans, GET_BY_ID, id_string);
     if (!child.good()) {
       NOTREACHED();
       return false;
     }
     if (child.GetIsDir()) {
       Id child_id_string = child.GetFirstChildId();
       // Traverse the children.
@@ skipping 188 matching lines @@
     encrypted_types.Put(FAVICON_TRACKING);
   if (nigori.encrypt_articles())
     encrypted_types.Put(ARTICLES);
   if (nigori.encrypt_app_list())
     encrypted_types.Put(APP_LIST);
   return encrypted_types;
 }
 
 }  // namespace syncable
 }  // namespace syncer