Avoid leaking objects between isolated worlds via attribute event listeners

Source/core/dom/EventListener.h

Index: Source/core/dom/EventListener.h
diff --git a/Source/core/dom/EventListener.h b/Source/core/dom/EventListener.h
index 1708a73c3fcca671b3ab163b0ccd0c955dd74f73..a1add8c6dc8f896b2d1459b0848841fbba7b3779 100644
--- a/Source/core/dom/EventListener.h
+++ b/Source/core/dom/EventListener.h
@@ -25,8 +25,9 @@
 
 namespace WebCore {
 
-    class ScriptExecutionContext;
+    class DOMWrapperWorld;
     class Event;
+    class ScriptExecutionContext;
 
     class EventListener : public RefCounted<EventListener> {
     public:
@@ -45,6 +46,7 @@ namespace WebCore {
         virtual bool operator==(const EventListener&) = 0;
         virtual void handleEvent(ScriptExecutionContext*, Event*) = 0;
         virtual bool wasCreatedFromMarkup() const { return false; }
+        virtual DOMWrapperWorld* world() const { return 0; }
 
         bool isAttribute() const { return virtualisAttribute(); }
         Type type() const { return m_type; }