chrome: Cleanup class/struct forward declarations

chrome/browser/ui/views/toolbar/back_button.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 CHROME_BROWSER_UI_VIEWS_TOOLBAR_BACK_BUTTON_H_
 #define CHROME_BROWSER_UI_VIEWS_TOOLBAR_BACK_BUTTON_H_
 
 #include "base/macros.h"
 #include "chrome/browser/ui/views/toolbar/toolbar_button.h"
 
 namespace ui {
 class MenuModel;
 }
 
 namespace views {
-class Border;
 class ButtonListener;
 }
 
 // A subclass of ToolbarButton to allow the back button's hit test region to
 // extend all the way to the start of the toolbar (i.e. the screen edge) in
 // maximized mode, to benefit from Fitt's Law.  The button images and focus
 // border are still drawn with the normal square shape.
 class BackButton : public ToolbarButton {
  public:
   // Takes ownership of the |model|, which can be null if no menu
@@ skipping 15 matching lines @@
   gfx::Rect GetThemePaintRect() const override;
 
   // Any leading margin to be applied. Used when the back button is in
   // a maximized state to extend to the full window width.
   int margin_leading_;
 
   DISALLOW_COPY_AND_ASSIGN(BackButton);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_TOOLBAR_BACK_BUTTON_H_