Return const by ref instead of value

ash/system/tray/system_tray_delegate.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 ASH_SYSTEM_TRAY_SYSTEM_TRAY_DELEGATE_H_
 #define ASH_SYSTEM_TRAY_SYSTEM_TRAY_DELEGATE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 123 matching lines @@
   // Returns true if system tray should be visible on startup.
   virtual bool GetTrayVisibilityOnStartup();
 
   // Gets information about the active user.
   virtual user::LoginStatus GetUserLoginStatus() const;
 
   // Shows UI for changing user's profile picture.
   virtual void ChangeProfilePicture();
 
   // Returns the domain that manages the device, if it is enterprise-enrolled.
-  virtual const std::string GetEnterpriseDomain() const;
+  virtual std::string GetEnterpriseDomain() const;
 
   // Returns notification for enterprise enrolled devices.
   virtual const base::string16 GetEnterpriseMessage() const;
 
   // Returns the display email of the user that manages the current supervised
   // user.
   virtual const std::string GetSupervisedUserManager() const;
 
   // Returns the name of the user that manages the current supervised user.
   virtual const base::string16 GetSupervisedUserManagerName() const;
@@ skipping 180 matching lines @@
   // asynchronously calls |callback| once a trusted policy becomes available.
   virtual void ShouldRebootOnShutdown(const RebootOnShutdownCallback& callback);
 
   // Returns VPNDelegate. May return nullptr.
   virtual VPNDelegate* GetVPNDelegate() const;
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_SYSTEM_TRAY_DELEGATE_H_