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

chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.h

 // Copyright (c) 2011 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_WEBUI_NTP_NEW_TAB_PAGE_SYNC_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_NTP_NEW_TAB_PAGE_SYNC_HANDLER_H_
 
 #include <string>
 
 #include "base/prefs/pref_change_registrar.h"
@@ skipping 31 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(NewTabPageSyncHandlerBrowserTest,
                            ChangeSigninAllowedToFalse);
 
   enum MessageType {
     HIDE,
     SYNC_ERROR,
     SYNC_PROMO
   };
   // Helper to invoke the |syncMessageChanged| JS function on the new tab page.
   virtual void SendSyncMessageToPage(MessageType type,
-                                     std::string msg, std::string linktext);
+                                     const std::string& msg,
+                                     const std::string& linktext);
 
   // Helper to query the sync service and figure out what to send to
   // the page, and send it via SendSyncMessageToPage.
   // NOTE: precondition: sync must be enabled.
   void BuildAndSendSyncStatus();
 
   // Helper to send a message to the NNTP which hides the sync section.
   void HideSyncStatusSection();
 
   // Helper to convert from a sync status message type to an NTP specific one.
   static MessageType FromSyncStatusMessageType(
       sync_ui_util::MessageType type);
 
   // Cached pointer to ProfileSyncService.
   ProfileSyncService* sync_service_;
 
   PrefChangeRegistrar profile_pref_registrar_;
 
   // Used to make sure we don't register ourselves twice if the user refreshes
   // the new tab page.
   bool waiting_for_initial_page_load_;
 
   DISALLOW_COPY_AND_ASSIGN(NewTabPageSyncHandler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_NTP_NEW_TAB_PAGE_SYNC_HANDLER_H_