Initial draft - modify ViewportAnchor to know about both inner and outer viewports.

Source/platform/scroll/ScrollView.h

 /*
  * Copyright (C) 2004, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Holger Hans Peter Freyther
  *
  * 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
@@ skipping 37 matching lines @@
     // ScrollableArea functions.
     virtual int scrollSize(ScrollbarOrientation) const OVERRIDE;
     virtual void setScrollOffset(const IntPoint&) OVERRIDE;
     virtual bool isScrollCornerVisible() const OVERRIDE;
     virtual void scrollbarStyleChanged() OVERRIDE;
     virtual bool userInputScrollable(ScrollbarOrientation) const OVERRIDE;
     virtual bool shouldPlaceVerticalScrollbarOnLeft() const OVERRIDE;
 
     virtual void notifyPageThatContentAreaWillPaint() const;
 
-    // NOTE: This should only be called by the overriden setScrollOffset from ScrollableArea.
-    virtual void scrollTo(const IntSize& newOffset);
-
     // The window that hosts the ScrollView. The ScrollView will communicate scrolls and repaints to the
     // host window in the window's coordinate space.
     virtual HostWindow* hostWindow() const = 0;
 
     // Returns a clip rect in host window coordinates. Used to clip the blit on a scroll.
     virtual IntRect windowClipRect(IncludeScrollbarsInRect = ExcludeScrollbars) const = 0;
 
     // Functions for child manipulation and inspection.
     const HashSet<RefPtr<Widget> >* children() const { return &m_children; }
     virtual void addChild(PassRefPtr<Widget>);
@@ skipping 180 matching lines @@
     virtual IntPoint convertFromContainingViewToScrollbar(const Scrollbar*, const IntPoint&) const OVERRIDE;
 
     void calculateAndPaintOverhangAreas(GraphicsContext*, const IntRect& dirtyRect);
     void calculateAndPaintOverhangBackground(GraphicsContext*, const IntRect& dirtyRect);
 
     virtual bool isScrollView() const OVERRIDE FINAL { return true; }
 
 protected:
     ScrollView();
 
+    // NOTE: This should only be called by the overriden setScrollOffset from ScrollableArea.
+    virtual void scrollTo(const IntSize& newOffset);
+
     virtual void contentRectangleForPaintInvalidation(const IntRect&);
     virtual void paintContents(GraphicsContext*, const IntRect& damageRect) = 0;
 
     virtual void paintOverhangAreas(GraphicsContext*, const IntRect& horizontalOverhangArea, const IntRect& verticalOverhangArea, const IntRect& dirtyRect);
 
     virtual void scrollbarExistenceDidChange() = 0;
     // These functions are used to create/destroy scrollbars.
     void setHasHorizontalScrollbar(bool);
     void setHasVerticalScrollbar(bool);
 
@@ skipping 70 matching lines @@
 
     void calculateOverhangAreasForPainting(IntRect& horizontalOverhangRect, IntRect& verticalOverhangRect);
     void updateOverhangAreas();
 }; // class ScrollView
 
 DEFINE_TYPE_CASTS(ScrollView, Widget, widget, widget->isScrollView(), widget.isScrollView());
 
 } // namespace blink
 
 #endif // ScrollView_h