Fix clippingContainer for fixed position elements

Source/core/rendering/RenderObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 688 matching lines @@
 
     // Set the style of the object if it's generated content.
     void setPseudoStyle(PassRefPtr<RenderStyle>);
 
     // Updates only the local style ptr of the object.  Does not update the state of the object,
     // and so only should be called when the style is known not to have changed (or from setStyle).
     void setStyleInternal(PassRefPtr<RenderStyle> style) { m_style = style; }
 
     // returns the containing block level element for this element.
     RenderBlock* containingBlock() const;
-    RenderObject* clippingContainer() const;
+    RenderObject* clippingContainer();
 
     bool canContainFixedPositionObjects() const
     {
         return isRenderView() || (hasTransform() && isRenderBlock()) || isSVGForeignObject() || isOutOfFlowRenderFlowThread();
     }
     bool canContainAbsolutePositionObjects() const
     {
         return isRenderView() || (hasTransform() && isRenderBlock()) || isSVGForeignObject();
     }
 
@@ skipping 690 matching lines @@
 void showTree(const WebCore::RenderObject*);
 void showLineTree(const WebCore::RenderObject*);
 void showRenderTree(const WebCore::RenderObject* object1);
 // We don't make object2 an optional parameter so that showRenderTree
 // can be called from gdb easily.
 void showRenderTree(const WebCore::RenderObject* object1, const WebCore::RenderObject* object2);
 
 #endif
 
 #endif // RenderObject_h