Factor painting code out of RenderBox into a new class called BoxPainter.

Source/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 826 matching lines @@
     }
 
     if (!o || !o->isRenderBlock())
         return 0; // This can still happen in case of an orphaned tree
 
     return toRenderBlock(o);
 }
 
 bool RenderObject::canRenderBorderImage() const
 {
-    ASSERT(style()->hasBorder());
+    if (!style()->hasBorder())
+        return false;
 
     StyleImage* borderImage = style()->borderImage().image();
     return borderImage && borderImage->canRender(*this, style()->effectiveZoom()) && borderImage->isLoaded();
 }
 
 bool RenderObject::mustInvalidateFillLayersPaintOnWidthChange(const FillLayer& layer) const
 {
     // Nobody will use multiple layers without wanting fancy positioning.
     if (layer.next())
         return true;
@@ skipping 2597 matching lines @@
 {
     if (object1) {
         const blink::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif