ui: Cleanup class/struct forward declarations

ui/gfx/native_widget_types.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 UI_GFX_NATIVE_WIDGET_TYPES_H_
 #define UI_GFX_NATIVE_WIDGET_TYPES_H_
 
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 21 matching lines @@
 //     NativeViewIds from the renderer and NativeViews.
 //
 //   NativeImage: The platform-specific image type used for drawing UI elements
 //     in the browser.
 //
 // The name 'View' here meshes with OS X where the UI elements are called
 // 'views' and with our Chrome UI code where the elements are also called
 // 'views'.
 
 #if defined(USE_AURA)
-class SkRegion;
 namespace aura {
 class Window;
 }
 namespace ui {
 class Cursor;
 class Event;
 }
 #endif  // defined(USE_AURA)
 
 #if defined(OS_WIN)
@@ skipping 150 matching lines @@
 #elif defined(USE_OZONE)
 typedef int32_t AcceleratedWidget;
 constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #else
 #error unknown platform
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_NATIVE_WIDGET_TYPES_H_