[Sync] Pass ModelTypeSet by value everywhere

sync/notifier/invalidation_util.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/notifier/invalidation_util.h"
 
 #include <ostream>
 #include <sstream>
 
 #include "base/json/json_writer.h"
@@ skipping 54 matching lines @@
 }
 
 std::string ObjectIdToString(
     const invalidation::ObjectId& object_id) {
   scoped_ptr<base::DictionaryValue> value(ObjectIdToValue(object_id));
   std::string str;
   base::JSONWriter::Write(value.get(), &str);
   return str;
 }
 
-ObjectIdSet ModelTypeSetToObjectIdSet(const ModelTypeSet& model_types) {
+ObjectIdSet ModelTypeSetToObjectIdSet(ModelTypeSet model_types) {
   ObjectIdSet ids;
   for (ModelTypeSet::Iterator it = model_types.First(); it.Good(); it.Inc()) {
     invalidation::ObjectId model_type_as_id;
     if (!RealModelTypeToObjectId(it.Get(), &model_type_as_id)) {
       DLOG(WARNING) << "Invalid model type " << it.Get();
       continue;
     }
     ids.insert(model_type_as_id);
   }
   return ids;
@@ skipping 16 matching lines @@
     const invalidation::Invalidation& invalidation) {
   std::stringstream ss;
   ss << "{ ";
   ss << "object_id: " << ObjectIdToString(invalidation.object_id()) << ", ";
   ss << "version: " << invalidation.version();
   ss << " }";
   return ss.str();
 }
 
 }  // namespace syncer