Cleanup: Pass std::string as const reference if possible

sync/test/fake_server/bookmark_entity.cc

 // Copyright 2014 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/test/fake_server/bookmark_entity.h"
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/guid.h"
@@ skipping 76 matching lines @@
       originator_cache_guid_(originator_cache_guid),
       originator_client_item_id_(originator_client_item_id),
       unique_position_(unique_position),
       is_folder_(is_folder),
       parent_id_(parent_id),
       creation_time_(creation_time),
       last_modified_time_(last_modified_time) {
   SetSpecifics(specifics);
 }
 
-void BookmarkEntity::SetParentId(string parent_id) {
+void BookmarkEntity::SetParentId(const string& parent_id) {
   parent_id_ = parent_id;
 }
 
 string BookmarkEntity::GetParentId() const {
   return parent_id_;
 }
 
 void BookmarkEntity::SerializeAsProto(sync_pb::SyncEntity* proto) const {
   FakeServerEntity::SerializeBaseProtoFields(proto);
 
   proto->set_originator_cache_guid(originator_cache_guid_);
   proto->set_originator_client_item_id(originator_client_item_id_);
 
   proto->set_parent_id_string(parent_id_);
   proto->set_ctime(creation_time_);
   proto->set_mtime(last_modified_time_);
 
   sync_pb::UniquePosition* unique_position = proto->mutable_unique_position();
   unique_position->CopyFrom(unique_position_);
 }
 
 bool BookmarkEntity::IsFolder() const {
   return is_folder_;
 }
 
 }  // namespace fake_server