Walk render tree instead of render layers for paint.

sky/engine/core/rendering/RenderBlock.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple 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 192 matching lines @@
         DefaultLayout,
         ForcedLayoutAfterContainingBlockMoved
     };
 
     void layoutPositionedObjects(bool relayoutChildren, PositionedLayoutBehavior = DefaultLayout);
 
     LayoutUnit marginIntrinsicLogicalWidthForChild(RenderBox* child) const;
 
     int beforeMarginInLineDirection(LineDirectionMode) const;
 
-    virtual void paint(PaintInfo&, const LayoutPoint&) override;
-    virtual void paintObject(PaintInfo&, const LayoutPoint&) override;
-    virtual void paintChildren(PaintInfo&, const LayoutPoint&);
+    virtual void paint(PaintInfo&, const LayoutPoint&, Vector<RenderBox*>& layers) override;
+    void paintObject(PaintInfo&, const LayoutPoint&, Vector<RenderBox*>& layers);
+    virtual void paintChildren(PaintInfo&, const LayoutPoint&, Vector<RenderBox*>& layers);
 
     virtual void adjustInlineDirectionLineBounds(unsigned /* expansionOpportunityCount */, float& /* logicalLeft */, float& /* logicalWidth */) const { }
 
     virtual void computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const override;
     virtual void computePreferredLogicalWidths() override;
 
     virtual int firstLineBoxBaseline() const override;
     virtual int inlineBlockBaseline(LineDirectionMode) const override;
     virtual int lastLineBoxBaseline(LineDirectionMode) const;
 
@@ skipping 90 matching lines @@
     // member variables out of RenderBlock and into RenderBlockFlow.
     friend class RenderBlockFlow;
     friend class RenderParagraph;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderBlock, isRenderBlock());
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_RENDERING_RENDERBLOCK_H_