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

Source/core/platform/Scrollbar.cpp

 /*
  * Copyright (C) 2004, 2006, 2008 Apple 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 83 matching lines @@
 Scrollbar::~Scrollbar()
 {
     if (AXObjectCache* cache = existingAXObjectCache())
         cache->remove(this);
 
     stopTimerIfNeeded();
 
     m_theme->unregisterScrollbar(this);
 }
 
+void Scrollbar::removeFromParent()
+{
+    if (parent())
+        toScrollView(parent())->removeChild(this);
+}
+
+ScrollView* Scrollbar::parentScrollView() const
+{
+    return toScrollView(parent());
+}
+
+ScrollView* Scrollbar::rootScrollView() const
+{
+    return toScrollView(root());
+}
+
 ScrollbarOverlayStyle Scrollbar::scrollbarOverlayStyle() const
 {
     return m_scrollableArea ? m_scrollableArea->scrollbarOverlayStyle() : ScrollbarOverlayStyleDefault;
 }
 
 void Scrollbar::getTickmarks(Vector<IntRect>& tickmarks) const
 {
     if (m_scrollableArea)
         m_scrollableArea->getTickmarks(tickmarks);
 }
@@ skipping 359 matching lines @@
 
     autoscrollPressedPart(theme()->initialAutoscrollTimerDelay());
 }
 
 void Scrollbar::setFrameRect(const IntRect& rect)
 {
     // Get our window resizer rect and see if we overlap. Adjust to avoid the overlap
     // if necessary.
     IntRect adjustedRect(rect);
     bool overlapsResizer = false;
-    ScrollView* view = parent();
+    ScrollView* view = parentScrollView();
     if (view && !rect.isEmpty() && !view->windowResizerRect().isEmpty()) {
         IntRect resizerRect = view->convertFromContainingWindow(view->windowResizerRect());
         if (rect.intersects(resizerRect)) {
             if (orientation() == HorizontalScrollbar) {
                 int overlap = rect.maxX() - resizerRect.x();
                 if (overlap > 0 && resizerRect.maxX() >= rect.maxX()) {
                     adjustedRect.setWidth(rect.width() - overlap);
                     overlapsResizer = true;
                 }
             } else {
                 int overlap = rect.maxY() - resizerRect.y();
                 if (overlap > 0 && resizerRect.maxY() >= rect.maxY()) {
                     adjustedRect.setHeight(rect.height() - overlap);
                     overlapsResizer = true;
                 }
             }
         }
     }
     if (overlapsResizer != m_overlapsResizer) {
         m_overlapsResizer = overlapsResizer;
         if (view)
             view->adjustScrollbarsAvoidingResizerCount(m_overlapsResizer ? 1 : -1);
     }
 
     Widget::setFrameRect(adjustedRect);
 }
 
-void Scrollbar::setParent(ScrollView* parentView)
+void Scrollbar::setParent(Widget* parentView)
 {
-    if (!parentView && m_overlapsResizer && parent())
-        parent()->adjustScrollbarsAvoidingResizerCount(-1);
+    if (!parentView && m_overlapsResizer && parentScrollView())
+        parentScrollView()->adjustScrollbarsAvoidingResizerCount(-1);
     Widget::setParent(parentView);
 }
 
 void Scrollbar::setEnabled(bool e)
 {
     if (m_enabled == e)
         return;
     m_enabled = e;
     theme()->updateEnabledState(this);
     invalidate();
@@ skipping 12 matching lines @@
     return m_scrollableArea->scrollAnimator()->shouldScrollbarParticipateInHitTesting(this);
 }
 
 bool Scrollbar::isWindowActive() const
 {
     return m_scrollableArea && m_scrollableArea->isActive();
 }
 
 AXObjectCache* Scrollbar::existingAXObjectCache() const
 {
-    if (!parent())
+    if (!parentScrollView())
         return 0;
 
-    return parent()->axObjectCache();
+    return parentScrollView()->axObjectCache();
 }
 
 void Scrollbar::invalidateRect(const IntRect& rect)
 {
     if (suppressInvalidation())
         return;
 
     if (m_scrollableArea)
         m_scrollableArea->invalidateScrollbar(this, rect);
 }
@@ skipping 35 matching lines @@
     if (!m_scrollableArea)
         return 0;
 
     if (m_orientation == HorizontalScrollbar)
         return m_scrollableArea->scrollPosition().x() - m_scrollableArea->minimumScrollPosition().x();
 
     return m_scrollableArea->scrollPosition().y() - m_scrollableArea->minimumScrollPosition().y();
 }
 
 } // namespace WebCore