Remove Widget's dependency upon its own inheritor aka ScrollView. This was nasty from an OO design…

Source/core/platform/Scrollbar.h

 /*
  * Copyright (C) 2004, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 17 matching lines @@
 
 #include "core/platform/Widget.h"
 #include "platform/Timer.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
 #include "wtf/MathExtras.h"
 #include "wtf/PassRefPtr.h"
 
 namespace WebCore {
 
+class AXObjectCache;
 class GraphicsContext;
 class IntRect;
 class PlatformGestureEvent;
 class PlatformMouseEvent;
 class ScrollableArea;
 class ScrollbarTheme;
+class ScrollView;
 
 class Scrollbar : public Widget,
                   public ScrollbarThemeClient {
 
 public:
     static PassRefPtr<Scrollbar> create(ScrollableArea*, ScrollbarOrientation, ScrollbarControlSize);
 
     virtual ~Scrollbar();
 
     // ScrollbarThemeClient implementation.
     virtual int x() const { return Widget::x(); }
     virtual int y() const { return Widget::y(); }
     virtual int width() const { return Widget::width(); }
     virtual int height() const { return Widget::height(); }
     virtual IntSize size() const { return Widget::size(); }
     virtual IntPoint location() const { return Widget::location(); }
 
-    virtual ScrollView* parent() const { return Widget::parent(); }
-    virtual ScrollView* root() const { return Widget::root(); }
+    virtual Widget* parent() const { return Widget::parent(); }
+    virtual Widget* root() const { return Widget::root(); }
+
+    void removeFromParent();
+    ScrollView* parentScrollView() const;
+    ScrollView* rootScrollView() const;
 
     virtual void setFrameRect(const IntRect&);
     virtual IntRect frameRect() const { return Widget::frameRect(); }
 
     virtual void invalidate() { Widget::invalidate(); }
     virtual void invalidateRect(const IntRect&);
 
     virtual ScrollbarOverlayStyle scrollbarOverlayStyle() const;
     virtual void getTickmarks(Vector<IntRect>&) const;
     virtual bool isScrollableAreaActive() const;
@@ skipping 130 matching lines @@
     ASSERT_WITH_SECURITY_IMPLICATION(!widget || widget->isScrollbar());
     return static_cast<const Scrollbar*>(widget);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toScrollbar(const Scrollbar*);
 
 } // namespace WebCore
 
 #endif // Scrollbar_h