Refactor root element background painting

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 988 matching lines @@
     bool shouldUseTransformFromContainer(const LayoutObject* container) const;
     void getTransformFromContainer(const LayoutObject* container, const LayoutSize& offsetInContainer, TransformationMatrix&) const;
 
     bool createsGroup() const { return isTransparent() || hasMask() || hasFilter() || style()->hasBlendMode(); }
 
     virtual void addFocusRingRects(Vector<LayoutRect>&, const LayoutPoint& additionalOffset) const { }
 
     // Compute a list of hit-test rectangles per layer rooted at this layoutObject.
     virtual void computeLayerHitTestRects(LayerHitTestRects&) const;
 
-    // Return the layoutObject whose background style is used to paint the root background. Should only be called on the layoutObject for which isDocumentElement() is true.
-    LayoutObject* layoutObjectForRootBackground();
-
     RespectImageOrientationEnum shouldRespectImageOrientation() const;
 
     bool isRelayoutBoundaryForInspector() const;
 
     // The previous paint invalidation rect in the object's previous paint backing.
     const LayoutRect& previousPaintInvalidationRect() const { return m_previousPaintInvalidationRect; }
     void setPreviousPaintInvalidationRect(const LayoutRect& rect) { m_previousPaintInvalidationRect = rect; }
 
     // The previous position of the top-left corner of the object in its previous paint backing.
     const LayoutPoint& previousPositionFromPaintInvalidationBacking() const { return m_previousPositionFromPaintInvalidationBacking; }
@@ skipping 644 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