Enable Null Syncable ID which is different than Root ID.

sync/internal_api/write_node.cc

 // 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.
 
 #include "sync/internal_api/public/write_node.h"
 
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "sync/internal_api/public/base_transaction.h"
@@ skipping 443 matching lines @@
   if (predecessor && predecessor->GetParentId() != new_parent.GetId()) {
     DCHECK(false);
     return false;
   }
 
   syncable::Id new_parent_id = new_parent.GetEntry()->GetId();
 
   // Filter out redundant changes if both the parent and the predecessor match.
   if (new_parent_id == entry_->GetParentId()) {
     const syncable::Id& old = entry_->GetPredecessorId();
-    if ((!predecessor && old.IsRoot()) ||
+    if ((!predecessor && old.IsNull()) ||
         (predecessor && (old == predecessor->GetEntry()->GetId()))) {
       return true;
     }
   }
 
   entry_->PutParentId(new_parent_id);
 
   // Now set the predecessor, which sets IS_UNSYNCED as necessary.
   return PutPredecessor(predecessor);
 }
@@ skipping 38 matching lines @@
   MarkForSyncing();
 
   return true;
 }
 
 void WriteNode::MarkForSyncing() {
   syncable::MarkForSyncing(entry_);
 }
 
 }  // namespace syncer