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

chrome/browser/extensions/api/system_indicator/system_indicator_manager.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_EXTENSIONS_API_SYSTEM_INDICATOR_SYSTEM_INDICATOR_MANAGER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INDICATOR_SYSTEM_INDICATOR_MANAGER_H_
 
 #include <map>
 #include <string>
 
@@ skipping 38 matching lines @@
                            UnloadedExtensionInfo::Reason reason) override;
 
   // ExtensionActionAPI::Observer implementation.
   void OnExtensionActionUpdated(
       ExtensionAction* extension_action,
       content::WebContents* web_contents,
       content::BrowserContext* browser_context) override;
 
   // Causes a call to OnStatusIconClicked for the specified extension_id.
   // Returns false if no ExtensionIndicatorIcon is found for the extension.
-  bool SendClickEventToExtensionForTest(const std::string extension_id);
+  bool SendClickEventToExtensionForTest(const std::string& extension_id);
 
   // Causes an indicator to be shown for the given extension_action.  Creates
   // the indicator if necessary.
   void CreateOrUpdateIndicator(
       const Extension* extension,
       ExtensionAction* extension_action);
 
   // Causes the indicator for the given extension to be hidden.
-  void RemoveIndicator(const std::string &extension_id);
+  void RemoveIndicator(const std::string& extension_id);
 
   typedef std::map<const std::string, linked_ptr<ExtensionIndicatorIcon> >
       SystemIndicatorMap;
 
   Profile* profile_;
   StatusTray* status_tray_;
   SystemIndicatorMap system_indicators_;
   base::ThreadChecker thread_checker_;
 
   ScopedObserver<ExtensionActionAPI, ExtensionActionAPI::Observer>
       extension_action_observer_;
 
   // Listen to extension unloaded notifications.
   ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
       extension_registry_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemIndicatorManager);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INDICATOR_SYSTEM_INDICATOR_MANAGER_H_