Enforcing that custom tag extensions have correct super classes.

Source/bindings/dart/DartUtilities.h

 // Copyright 2011, Google 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:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
@@ skipping 465 matching lines @@
 
     static Dart_Handle dateToDart(double);
     static double dartToDate(Dart_Handle, Dart_Handle&);
     static double dartToDate(Dart_NativeArguments args, int idx, Dart_Handle&);
     static bool isHtmlElement(DartDOMData*, Dart_Handle);
     static bool isDateTime(DartDOMData*, Dart_Handle);
     static bool isBlob(DartDOMData*, Dart_Handle);
     static bool isImageData(DartDOMData*, Dart_Handle);
     static bool isIDBKeyRange(DartDOMData*, Dart_Handle);
     static bool isTypeSubclassOf(Dart_Handle type, intptr_t libraryId, const char* typeName);
+    static bool isTypeSubclassOfTag(Dart_Handle type, const String& tagName);
     static bool objectIsType(Dart_Handle, Dart_Handle type);
 
     static bool isTypedData(Dart_Handle);
 
     static Dart_Handle arrayBufferToDart(WTF::ArrayBuffer*);
     static Dart_Handle arrayBufferToDart(PassRefPtr<WTF::ArrayBuffer> value)
     {
         return arrayBufferToDart(value.get());
     }
 
@@ skipping 154 matching lines @@
     }
 };
 
 
 #define DART_UNIMPLEMENTED_EXCEPTION() DartUtilities::notImplementedException(__FILE__, __LINE__)
 #define DART_UNIMPLEMENTED() Dart_ThrowException(DART_UNIMPLEMENTED_EXCEPTION());
 
 } // namespace WebCore
 
 #endif // DartUtilities_h