Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/RenderPart.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Simon Hausmann <hausmann@kde.org>
  * Copyright (C) 2006, 2009 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 33 matching lines @@
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) OVERRIDE;
 
 protected:
     virtual bool requiresLayer() const;
 
 private:
     virtual bool isRenderPart() const OVERRIDE FINAL { return true; }
     virtual const char* renderName() const { return "RenderPart"; }
 };
 
-inline RenderPart* toRenderPart(RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderPart());
-    return static_cast<RenderPart*>(object);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toRenderPart(const RenderPart*);
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderPart, isRenderPart());
 
 }
 
 #endif