ash: Cleanup class/struct forward declarations

ash/common/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_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_DELEGATE_H_
 #define ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_DELEGATE_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "ash/ash_export.h"
 #include "ash/common/login_status.h"
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
 #include "base/i18n/time_formatting.h"
 #include "base/strings/string16.h"
 
-class AccountId;
-
 namespace base {
 class TimeDelta;
 class TimeTicks;
 }
 
 namespace device {
 enum class BluetoothDeviceType;
 }
 
 namespace ash {
@@ skipping 190 matching lines @@
   // Creates a system tray item for display rotation lock.
   // TODO(jamescook): Remove this when mus has support for display management
   // and we have a DisplayManager equivalent. See http://crbug.com/548429
   virtual std::unique_ptr<SystemTrayItem> CreateRotationLockTrayItem(
       SystemTray* tray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_DELEGATE_H_