Return const by ref instead of value

ash/system/tray/system_tray_delegate.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 "ash/system/tray/system_tray_delegate.h"
 
 namespace ash {
 
 NetworkIconInfo::NetworkIconInfo()
     : connecting(false),
@@ skipping 49 matching lines @@
   return false;
 }
 
 user::LoginStatus SystemTrayDelegate::GetUserLoginStatus() const {
   return user::LOGGED_IN_NONE;
 }
 
 void SystemTrayDelegate::ChangeProfilePicture() {
 }
 
-const std::string SystemTrayDelegate::GetEnterpriseDomain() const {
+std::string SystemTrayDelegate::GetEnterpriseDomain() const {
   return std::string();
 }
 
 const base::string16 SystemTrayDelegate::GetEnterpriseMessage() const {
   return base::string16();
 }
 
 const std::string SystemTrayDelegate::GetSupervisedUserManager() const {
   return std::string();
 }
@@ skipping 200 matching lines @@
 
 void SystemTrayDelegate::ShouldRebootOnShutdown(
     const RebootOnShutdownCallback& callback) {
 }
 
 VPNDelegate* SystemTrayDelegate::GetVPNDelegate() const {
   return nullptr;
 }
 
 }  // namespace ash