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

chrome/browser/chromeos/input_method/input_method_manager_impl.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 CHROME_BROWSER_CHROMEOS_INPUT_METHOD_INPUT_METHOD_MANAGER_IMPL_H_
 #define CHROME_BROWSER_CHROMEOS_INPUT_METHOD_INPUT_METHOD_MANAGER_IMPL_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 203 matching lines @@
   // Loads necessary component extensions.
   // TODO(nona): Support dynamical unloading.
   void LoadNecessaryComponentExtensions(StateImpl* state);
 
   // Starts or stops the system input method framework as needed.
   // (after list of enabled input methods has been updated).
   // If state is active, active input method is updated.
   void ReconfigureIMFramework(StateImpl* state);
 
   // Record input method usage histograms.
-  void RecordInputMethodUsage(std::string input_method_id);
+  void RecordInputMethodUsage(const std::string& input_method_id);
 
   scoped_ptr<InputMethodDelegate> delegate_;
 
   // The current UI session status.
   UISessionState ui_session_;
 
   // A list of objects that monitor the manager.
   base::ObserverList<InputMethodManager::Observer> observers_;
   base::ObserverList<CandidateWindowObserver> candidate_window_observers_;
 
@@ skipping 23 matching lines @@
   typedef std::map<Profile*, EngineMap, ProfileCompare> ProfileEngineMap;
   ProfileEngineMap engine_map_;
 
   DISALLOW_COPY_AND_ASSIGN(InputMethodManagerImpl);
 };
 
 }  // namespace input_method
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_INPUT_METHOD_INPUT_METHOD_MANAGER_IMPL_H_