Remove enable Drive offline system tray UI.

ash/system/drive/tray_drive.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_DRIVE_TRAY_DRIVE_H_
 #define ASH_SYSTEM_DRIVE_TRAY_DRIVE_H_
 
 #include "ash/system/drive/drive_observer.h"
 #include "ash/system/tray/tray_image_item.h"
 #include "base/timer/timer.h"
@@ skipping 23 matching lines @@
 
   // Overridden from SystemTrayItem.
   virtual views::View* CreateDefaultView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateDetailedView(user::LoginStatus status) OVERRIDE;
   virtual void DestroyDefaultView() OVERRIDE;
   virtual void DestroyDetailedView() OVERRIDE;
   virtual void UpdateAfterLoginStatusChange(user::LoginStatus status) OVERRIDE;
 
   // Overridden from DriveObserver.
   virtual void OnDriveJobUpdated(const DriveOperationStatus& status) OVERRIDE;
-  virtual void OnDriveOfflineEnabled() OVERRIDE;
 
   // Delayed hiding of the tray item after encountering an empty operation list.
   void HideIfNoOperations();
 
   tray::DriveDefaultView* default_;
   tray::DriveDetailedView* detailed_;
   base::OneShotTimer<TrayDrive> hide_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayDrive);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_DRIVE_TRAY_DRIVE_H_