Virtualize EventDispatchMediator creation and cleanup calling.

Source/core/events/Event.cpp

Index: Source/core/events/Event.cpp
diff --git a/Source/core/events/Event.cpp b/Source/core/events/Event.cpp
index 9a777f355c17ce80858f7307e0fd0cdc2df06672..397206955ee51cc1b58b90afd82fecdd231726e3 100644
--- a/Source/core/events/Event.cpp
+++ b/Source/core/events/Event.cpp
@@ -24,6 +24,7 @@
 #include "core/events/Event.h"
 
 #include "core/dom/StaticNodeList.h"
+#include "core/events/EventDispatchMediator.h"
 #include "core/events/EventTarget.h"
 #include "core/frame/OriginsUsingFeatures.h"
 #include "core/frame/UseCounter.h"
@@ -237,6 +238,11 @@ WillBeHeapVector<RefPtrWillBeMember<EventTarget>> Event::path(ScriptState* scrip
     return WillBeHeapVector<RefPtrWillBeMember<EventTarget>>();
 }
 
+PassRefPtrWillBeRawPtr<EventDispatchMediator> Event::createMediator()
+{
+    return EventDispatchMediator::create(this);
+}
+
 EventTarget* Event::currentTarget() const
 {
     if (!m_currentTarget)