Inherit EventTarget interface instead of duplicating its code

Source/bindings/v8/custom/V8MutationObserverCustom.cpp

Index: Source/bindings/v8/custom/V8MutationObserverCustom.cpp
diff --git a/Source/bindings/v8/custom/V8MutationObserverCustom.cpp b/Source/bindings/v8/custom/V8MutationObserverCustom.cpp
index 24cc5a208da4e93c7b93b474fca6b61ab5c91689..7547dac81a7860d067bc605c83eee40796fd883b 100644
--- a/Source/bindings/v8/custom/V8MutationObserverCustom.cpp
+++ b/Source/bindings/v8/custom/V8MutationObserverCustom.cpp
@@ -60,7 +60,7 @@ void V8MutationObserver::constructorCustom(const v8::FunctionCallbackInfo<v8::Va
     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);
 }