sync: we can't lookup empty client tag nodes, so don't allow creating them

chrome/browser/sync/internal_api/write_node.cc

 // Copyright (c) 2011 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 "chrome/browser/sync/internal_api/write_node.h"
 
 #include "base/json/json_writer.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/sync/engine/nigori_util.h"
@@ skipping 376 matching lines @@
 // Create a new node with default properties and a client defined unique tag,
 // and bind this WriteNode to it.
 // Return true on success. If the tag exists in the database, then
 // we will attempt to undelete the node.
 // TODO(chron): Code datatype into hash tag.
 // TODO(chron): Is model type ever lost?
 bool WriteNode::InitUniqueByCreation(syncable::ModelType model_type,
                                      const BaseNode& parent,
                                      const std::string& tag) {
   DCHECK(!entry_) << "Init called twice";
+  if (tag.empty()) {
+    LOG(WARNING) << "InitUniqueByCreation failed due to empty tag.";
+    return false;
+  }
 
   const std::string hash = GenerateSyncableHash(model_type, tag);
 
   syncable::Id parent_id = parent.GetEntry()->Get(syncable::ID);
 
   // Start out with a dummy name.  We expect
   // the caller to set a meaningful name after creation.
   string dummy(kDefaultNameForNewNodes);
 
   // Check if we have this locally and need to undelete it.
@@ skipping 110 matching lines @@
   sync_pb::BookmarkSpecifics new_value = GetBookmarkSpecifics();
   new_value.set_favicon(bytes.empty() ? NULL : &bytes[0], bytes.size());
   SetBookmarkSpecifics(new_value);
 }
 
 void WriteNode::MarkForSyncing() {
   syncable::MarkForSyncing(entry_);
 }
 
 } // namespace sync_api