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

chrome/browser/ui/ash/launcher/chrome_launcher_controller.h

 // Copyright 2013 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_UI_ASH_LAUNCHER_CHROME_LAUNCHER_CONTROLLER_H_
 #define CHROME_BROWSER_UI_ASH_LAUNCHER_CHROME_LAUNCHER_CONTROLLER_H_
 
 #include <list>
 #include <map>
 #include <set>
@@ skipping 334 matching lines @@
   void AdditionalUserAddedToSession(Profile* profile);
 
   // Get the list of all running incarnations of this item.
   // |event_flags| specifies the flags which were set by the event which
   // triggered this menu generation. It can be used to generate different lists.
   ChromeLauncherAppMenuItems GetApplicationList(const ash::ShelfItem& item,
                                                 int event_flags);
 
   // Get the list of all tabs which belong to a certain application type.
   std::vector<content::WebContents*> GetV1ApplicationsFromAppId(
-      std::string app_id);
+      const std::string& app_id);
 
   // Activates a specified shell application.
   void ActivateShellApp(const std::string& app_id, int index);
 
   // Checks if a given |web_contents| is known to be associated with an
   // application of type |app_id|.
   bool IsWebContentHandledByApplication(content::WebContents* web_contents,
                                         const std::string& app_id);
 
   // Check if the gMail app is loaded and it can handle the given web content.
@@ skipping 235 matching lines @@
   // The list of running & un-pinned applications for different users on hidden
   // desktops.
   typedef std::vector<std::string> RunningAppListIds;
   typedef std::map<std::string, RunningAppListIds> RunningAppListIdMap;
   RunningAppListIdMap last_used_running_application_order_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeLauncherController);
 };
 
 #endif  // CHROME_BROWSER_UI_ASH_LAUNCHER_CHROME_LAUNCHER_CONTROLLER_H_