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

Source/core/dom/MessagePort.cpp

Index: Source/core/dom/MessagePort.cpp
diff --git a/Source/core/dom/MessagePort.cpp b/Source/core/dom/MessagePort.cpp
index 0cb6ed60e13f862692180e444bd9ce9d3bd52d80..4ecd86d9b6094baedd9c9ab3a9a4089a98736711 100644
--- a/Source/core/dom/MessagePort.cpp
+++ b/Source/core/dom/MessagePort.cpp
@@ -197,7 +197,7 @@ void MessagePort::dispatchMessages()
             return;
 
         OwnPtr<MessagePortArray> ports = MessagePort::entanglePorts(*executionContext(), channels.release());
-        RefPtr<Event> evt = MessageEvent::create(ports.release(), message.release());
+        RefPtrWillBeRawPtr<Event> evt = MessageEvent::create(ports.release(), message.release());
 
         dispatchEvent(evt.release(), ASSERT_NO_EXCEPTION);
     }