Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/modules/websockets/CloseEvent.h

Index: Source/modules/websockets/CloseEvent.h
diff --git a/Source/modules/websockets/CloseEvent.h b/Source/modules/websockets/CloseEvent.h
index aab3c5ccd2dfaaa298f99e1eaed9a8e8cf5785ca..9256228214e474025856a9644235f21d47eeb92e 100644
--- a/Source/modules/websockets/CloseEvent.h
+++ b/Source/modules/websockets/CloseEvent.h
@@ -72,6 +72,8 @@ public:
     // Event function.
     virtual const AtomicString& interfaceName() const OVERRIDE { return EventNames::CloseEvent; }
 
+    virtual void trace(Visitor* visitor) OVERRIDE { Event::trace(visitor); }
+
 private:
     CloseEvent()
         : Event(EventTypeNames::close, false, false)