Refactor root element background painting

Source/core/layout/LayoutBoxModelObject.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 186 matching lines @@
     // The query rect is given in local coordinate system.
     virtual bool backgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const { return false; }
 
     virtual void invalidateTreeIfNeeded(PaintInvalidationState&) override;
 
     // Indicate that the contents of this layoutObject need to be repainted. Only has an effect if compositing is being used,
     void setBackingNeedsPaintInvalidationInRect(const LayoutRect&, PaintInvalidationReason) const; // r is in the coordinate space of this layout object
 
     void invalidateDisplayItemClientOnBacking(const DisplayItemClientWrapper&) const;
 
+    bool backgroundStolenForBeingBody() const;

[chrishtr, 2015/06/03 18:15:15]

Add comments explaining what this is about.

[trchen, 2015/06/03 23:15:24]

Acknowledged.

+
 protected:
     virtual void willBeDestroyed() override;
 
     LayoutPoint adjustedPositionRelativeToOffsetParent(const LayoutPoint&) const;
 
     bool calculateHasBoxDecorations() const;
 
     LayoutBoxModelObject* continuation() const;
     void setContinuation(LayoutBoxModelObject*);
 
@@ skipping 46 matching lines @@
     virtual bool isLayoutBoxModelObject() const override final { return true; }
 
     OwnPtr<DeprecatedPaintLayer> m_layer;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBoxModelObject, isBoxModelObject());
 
 } // namespace blink
 
 #endif // LayoutBoxModelObject_h