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

chrome/browser/extensions/api/system_indicator/system_indicator_manager.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/extensions/api/system_indicator/system_indicator_manager.h"
 
 #include "base/memory/linked_ptr.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/extensions/extension_action.h"
 #include "chrome/browser/profiles/profile.h"
@@ skipping 143 matching lines @@
     CreateOrUpdateIndicator(
         ExtensionRegistry::Get(profile_)->enabled_extensions().GetByID(
             extension_id),
         extension_action);
   } else {
     RemoveIndicator(extension_id);
   }
 }
 
 bool SystemIndicatorManager::SendClickEventToExtensionForTest(
-    const std::string extension_id) {
-
+    const std::string& extension_id) {
     extensions::SystemIndicatorManager::SystemIndicatorMap::iterator it =
         system_indicators_.find(extension_id);
 
     if (it == system_indicators_.end())
       return false;
 
     it->second->OnStatusIconClicked();
     return true;
 }
 
@@ skipping 12 matching lines @@
   if (extension_icon)
     system_indicators_[extension->id()] = make_linked_ptr(extension_icon);
 }
 
 void SystemIndicatorManager::RemoveIndicator(const std::string& extension_id) {
   DCHECK(thread_checker_.CalledOnValidThread());
   system_indicators_.erase(extension_id);
 }
 
 }  // namespace extensions