Cleanup: Pass std::string as const reference from rlz/

rlz/chromeos/lib/rlz_value_store_chromeos.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 RLZ_CHROMEOS_LIB_RLZ_VALUE_STORE_CHROMEOS_H_
 #define RLZ_CHROMEOS_LIB_RLZ_VALUE_STORE_CHROMEOS_H_
 
 #include "base/files/file_path.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/values.h"
@@ skipping 46 matching lines @@
   void CollectGarbage() override;
 
  private:
   // Reads RLZ store from file.
   void ReadStore();
 
   // Writes RLZ store back to file.
   void WriteStore();
 
   // Adds |value| to list at |list_name| path in JSON store.
-  bool AddValueToList(std::string list_name, base::Value* value);
+  bool AddValueToList(const std::string& list_name, base::Value* value);
   // Removes |value| from list at |list_name| path in JSON store.
-  bool RemoveValueFromList(std::string list_name, const base::Value& value);
+  bool RemoveValueFromList(const std::string& list_name,
+                           const base::Value& value);
 
   // In-memory store with RLZ data.
   scoped_ptr<base::DictionaryValue> rlz_store_;
 
   base::FilePath store_path_;
 
   bool read_only_;
 
   DISALLOW_COPY_AND_ASSIGN(RlzValueStoreChromeOS);
 };
 
 }  // namespace rlz_lib
 
 #endif  // RLZ_CHROMEOS_LIB_RLZ_VALUE_STORE_CHROMEOS_H_