Introduce DEFINE_AX_OBJECT_TYPE_CASTS to replace manual toFoo() in accessibility child class

Source/core/accessibility/AXSVGRoot.h

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 32 matching lines @@
 
     void setParent(AXObject* parent) { m_parent = parent; }
 
 private:
     AXObject* m_parent;
 
     virtual AXObject* parentObject() const OVERRIDE;
     virtual bool isAXSVGRoot() const OVERRIDE { return true; }
 };
 
-inline AXSVGRoot* toAXSVGRoot(AXObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isAXSVGRoot());
-    return static_cast<AXSVGRoot*>(object);
-}
+DEFINE_AX_OBJECT_TYPE_CASTS(AXSVGRoot, isAXSVGRoot());
 
 } // namespace WebCore
 
 #endif // AXSVGRoot_h