Inherit EventTarget interface instead of duplicating its code

Source/bindings/v8/custom/V8MutationObserverCustom.cpp

 /*
  * Copyright (C) 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 42 matching lines @@
         throwTypeError("Callback argument must be a function", args.GetIsolate());
         return;
     }
 
     ScriptExecutionContext* context = getScriptExecutionContext();
     v8::Handle<v8::Object> wrapper = args.Holder();
 
     RefPtr<MutationCallback> callback = V8MutationCallback::create(v8::Handle<v8::Function>::Cast(arg), context, wrapper, args.GetIsolate());
     RefPtr<MutationObserver> observer = MutationObserver::create(callback.release());
 
-    V8DOMWrapper::associateObjectWithWrapper(observer.release(), &info, wrapper, args.GetIsolate(), WrapperConfiguration::Dependent);
+    V8DOMWrapper::associateObjectWithWrapper<V8MutationObserver>(observer.release(), &info, wrapper, args.GetIsolate(), WrapperConfiguration::Dependent);
     args.GetReturnValue().Set(wrapper);
 }
 
 } // namespace WebCore