Remove const qualifier from function return type.

ash/system/tray/default_system_tray_delegate.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 ASH_SYSTEM_TRAY_DEFAULT_SYSTEM_TRAY_DELEGATE_H_
 #define ASH_SYSTEM_TRAY_DEFAULT_SYSTEM_TRAY_DELEGATE_H_
 
 #include "ash/ash_export.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace ash {
 
 class ASH_EXPORT DefaultSystemTrayDelegate : public SystemTrayDelegate {
  public:
   DefaultSystemTrayDelegate();
   ~DefaultSystemTrayDelegate() override;
 
   // SystemTrayDelegate
   bool GetTrayVisibilityOnStartup() override;
   user::LoginStatus GetUserLoginStatus() const override;
-  const std::string GetSupervisedUserManager() const override;
+  std::string GetSupervisedUserManager() const override;
   bool IsUserSupervised() const override;
   void GetSystemUpdateInfo(UpdateInfo* info) const override;
   bool ShouldShowSettings() override;
   bool ShouldShowDisplayNotification() override;
   void ToggleBluetooth() override;
   bool IsBluetoothDiscovering() override;
   bool GetBluetoothAvailable() override;
   bool GetBluetoothEnabled() override;
   bool GetBluetoothDiscovering() override;
   VolumeControlDelegate* GetVolumeControlDelegate() const override;
   void SetVolumeControlDelegate(
       scoped_ptr<VolumeControlDelegate> delegate) override;
   int GetSystemTrayMenuWidth() override;
 
  private:
   bool bluetooth_enabled_;
   scoped_ptr<VolumeControlDelegate> volume_control_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultSystemTrayDelegate);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_DEFAULT_SYSTEM_TRAY_DELEGATE_H_