[Sync] Pass ModelTypeSet by value everywhere

sync/engine/verify_updates_command.h

 // 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.
 
 #ifndef SYNC_ENGINE_VERIFY_UPDATES_COMMAND_H_
 #define SYNC_ENGINE_VERIFY_UPDATES_COMMAND_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "sync/engine/model_changing_syncer_command.h"
@@ skipping 20 matching lines @@
   virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
   struct VerifyUpdateResult {
     VerifyResult value;
     ModelSafeGroup placement;
   };
   VerifyUpdateResult VerifyUpdate(syncable::WriteTransaction* trans,
                                   const sync_pb::SyncEntity& entry,
-                                  const ModelTypeSet& requested_types,
+                                  ModelTypeSet requested_types,
                                   const ModelSafeRoutingInfo& routes);
   DISALLOW_COPY_AND_ASSIGN(VerifyUpdatesCommand);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_VERIFY_UPDATES_COMMAND_H_