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

Source/core/events/FocusEvent.cpp

Index: Source/core/events/FocusEvent.cpp
diff --git a/Source/core/events/FocusEvent.cpp b/Source/core/events/FocusEvent.cpp
index 5949a3ecfb9d12265e2c833ad2840ac0abd08a60..8cae98eca9420a875cac0a844178dbe16e199b44 100644
--- a/Source/core/events/FocusEvent.cpp
+++ b/Source/core/events/FocusEvent.cpp
@@ -66,6 +66,11 @@ FocusEvent::FocusEvent(const AtomicString& type, const FocusEventInit& initializ
     ScriptWrappable::init(this);
 }
 
+void FocusEvent::trace(Visitor* visitor)
+{
+    UIEvent::trace(visitor);
+}
+
 PassRefPtr<FocusEventDispatchMediator> FocusEventDispatchMediator::create(PassRefPtr<FocusEvent> focusEvent)
 {
     return adoptRef(new FocusEventDispatchMediator(focusEvent));