Reduce repetitive EventTarget subclassing

Source/core/events/EventTarget.cpp

Index: Source/core/events/EventTarget.cpp
diff --git a/Source/core/events/EventTarget.cpp b/Source/core/events/EventTarget.cpp
index 6c61e0d5dccf934e2404b9187b1a065680666c60..b3822d15e97ae0e584ea517265a2fd471db754e4 100644
--- a/Source/core/events/EventTarget.cpp
+++ b/Source/core/events/EventTarget.cpp
@@ -83,8 +83,7 @@ inline DOMWindow* EventTarget::executingWindow()
 
 bool EventTarget::addEventListener(const AtomicString& eventType, PassRefPtr<EventListener> listener, bool useCapture)
 {
-    EventTargetData* d = ensureEventTargetData();
-    return d->eventListenerMap.add(eventType, listener, useCapture);
+    return ensureEventTargetData().eventListenerMap.add(eventType, listener, useCapture);
 }
 
 bool EventTarget::removeEventListener(const AtomicString& eventType, EventListener* listener, bool useCapture)