ui: Cleanup class/struct forward declarations

ui/views/style/platform_style.h

 // Copyright 2015 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 UI_VIEWS_STYLE_PLATFORM_STYLE_H_
 #define UI_VIEWS_STYLE_PLATFORM_STYLE_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/controls/button/custom_button.h"
 #include "ui/views/controls/combobox/combobox.h"
 #include "ui/views/views_export.h"
 
 namespace views {
 
 class Border;
-class FocusableBorder;
 class Label;
 class LabelButton;
 class ScrollBar;
 
 // Cross-platform API for providing platform-specific styling for toolkit-views.
 class VIEWS_EXPORT PlatformStyle {
  public:
   // Type used by LabelButton to map button states to text colors.
   using ButtonColorByState = SkColor[Button::STATE_COUNT];
 
@@ skipping 56 matching lines @@
   // the failed edit if platform-appropriate.
   static void OnTextfieldEditFailed();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformStyle);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_STYLE_PLATFORM_STYLE_H_