ash: Cleanup class/struct forward declarations

ash/shell/panel_window.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_SHELL_PANEL_WINDOW_H_
 #define ASH_SHELL_PANEL_WINDOW_H_
 
 #include "base/macros.h"
 #include "ui/aura/aura_export.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/widget/widget_delegate.h"
 
 namespace ash {
 
-class PanelFrameView;
-
 // Example Class for panel windows (Widget::InitParams::TYPE_PANEL).
 // Instances of PanelWindow will get added to the PanelContainer top level
 // window which manages the panel layout through PanelLayoutManager.
 class PanelWindow : public views::WidgetDelegateView {
  public:
   explicit PanelWindow(const std::string& name);
   ~PanelWindow() override;
 
   // Creates the widget for the panel window using |params_|.
   views::Widget* CreateWidget();
@@ skipping 19 matching lines @@
 
   std::string name_;
   views::Widget::InitParams params_;
 
   DISALLOW_COPY_AND_ASSIGN(PanelWindow);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_PANEL_WINDOW_H_