ui: Cleanup class/struct forward declarations

ui/base/base_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 UI_BASE_BASE_WINDOW_H_
 #define UI_BASE_BASE_WINDOW_H_
 
 #include "base/compiler_specific.h"
 #include "ui/base/ui_base_types.h"  // WindowShowState
 #include "ui/gfx/native_widget_types.h"
 
 namespace gfx {
 class Rect;
 }
 
-class SkRegion;
-
 namespace ui {
 
 // Provides an interface to perform actions on windows, and query window
 // state.
 class UI_BASE_EXPORT BaseWindow {
  public:
   // Returns true if the window is currently the active/focused window.
   virtual bool IsActive() const = 0;
 
   // Returns true if the window is maximized (aka zoomed).
@@ skipping 62 matching lines @@
   virtual bool IsAlwaysOnTop() const = 0;
 
   // If set to true, the window will stay on top of other windows which do not
   // have this flag enabled.
   virtual void SetAlwaysOnTop(bool always_on_top) = 0;
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_BASE_WINDOW_H_