Oilpan: Replace most of RefPtrs for Event objects with oilpan's transition types

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 03756cc13284d294058fa9cfc0dfd9419794fc70..6d278317771fa4d77975a84c681759540d6a5556 100644
--- a/Source/core/events/Event.cpp
+++ b/Source/core/events/Event.cpp
@@ -180,7 +180,7 @@ void Event::receivedTarget()
 {
 }
 
-void Event::setUnderlyingEvent(PassRefPtr<Event> ue)
+void Event::setUnderlyingEvent(PassRefPtrWillBeRawPtr<Event> ue)
 {
     // Prohibit creation of a cycle -- just do nothing in that case.
     for (Event* e = ue.get(); e; e = e->underlyingEvent())
@@ -213,8 +213,9 @@ PassRefPtr<NodeList> Event::path() const
     return StaticNodeList::createEmpty();
 }
 
-void Event::trace(Visitor*)
+void Event::trace(Visitor* visitor)
 {
+    visitor->trace(m_underlyingEvent);
 }
 
 } // namespace WebCore