Ensure that positioned objects' list is always in parent first order

Source/core/layout/LayoutObject.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 720 matching lines @@
     void setStyle(PassRefPtr<ComputedStyle>);
 
     // Set the style of the object if it's generated content.
     void setPseudoStyle(PassRefPtr<ComputedStyle>);
 
     // 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<ComputedStyle> style) { m_style = style; }
 
     // returns the containing block level element for this element.
-    LayoutBlock* containingBlock() const;
+    LayoutBlock* containingBlock(const ComputedStyle* overrideStyle = nullptr) const;
 
     bool canContainFixedPositionObjects() const
     {
         return isLayoutView() || (hasTransformRelatedProperty() && isLayoutBlock()) || isSVGForeignObject();
     }
 
     // Convert the given local point to absolute coordinates
     // FIXME: Temporary. If UseTransforms is true, take transforms into account. Eventually localToAbsolute() will always be transform-aware.
     FloatPoint localToAbsolute(const FloatPoint& localPoint = FloatPoint(), MapCoordinatesFlags = 0) const;
     FloatPoint absoluteToLocal(const FloatPoint&, MapCoordinatesFlags = 0) const;
@@ skipping 911 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h