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

Source/core/accessibility/AXScrollView.h

 /*
  * Copyright (C) 2011 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 63 matching lines @@
     virtual AXObject* firstChild() const OVERRIDE { return webAreaObject(); }
     AXScrollbar* addChildScrollbar(Scrollbar*);
     void removeChildScrollbar(AXObject*);
 
     ScrollView* m_scrollView;
     RefPtr<AXObject> m_horizontalScrollbar;
     RefPtr<AXObject> m_verticalScrollbar;
     bool m_childrenDirty;
 };
 
-inline AXScrollView* toAXScrollView(AXObject* object)
-{
-    ASSERT(!object || object->isAXScrollView());
-    if (!object->isAXScrollView())
-        return 0;
-
-    return static_cast<AXScrollView*>(object);
-}
+DEFINE_AX_OBJECT_TYPE_CASTS(AXScrollView, isAXScrollView());
 
 } // namespace WebCore
 
 #endif // AXScrollView_h