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

chrome/browser/chromeos/input_method/input_method_manager_impl.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 "chrome/browser/chromeos/input_method/input_method_manager_impl.h"
 
 #include <algorithm>  // std::find
 
 #include <sstream>
 
@@ skipping 853 matching lines @@
       component_extension_ime_manager_->GetAllIMEAsInputMethodDescriptor();
   util_.ResetInputMethods(descriptors);
 }
 
 InputMethodManagerImpl::~InputMethodManagerImpl() {
   if (candidate_window_controller_.get())
     candidate_window_controller_->RemoveObserver(this);
 }
 
 void InputMethodManagerImpl::RecordInputMethodUsage(
-    std::string input_method_id) {
+    const std::string& input_method_id) {
   UMA_HISTOGRAM_ENUMERATION("InputMethod.Category",
                             GetInputMethodCategory(input_method_id),
                             INPUT_METHOD_CATEGORY_MAX);
   UMA_HISTOGRAM_SPARSE_SLOWLY(
       "InputMethod.ID2", static_cast<int32_t>(base::Hash(input_method_id)));
 }
 
 void InputMethodManagerImpl::AddObserver(
     InputMethodManager::Observer* observer) {
   observers_.AddObserver(observer);
@@ skipping 272 matching lines @@
   if (candidate_window_controller_.get())
     return;
 
   candidate_window_controller_.reset(
       CandidateWindowController::CreateCandidateWindowController());
   candidate_window_controller_->AddObserver(this);
 }
 
 }  // namespace input_method
 }  // namespace chromeos