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

Source/modules/mediasource/WebKitSourceBufferList.cpp

Index: Source/modules/mediasource/WebKitSourceBufferList.cpp
diff --git a/Source/modules/mediasource/WebKitSourceBufferList.cpp b/Source/modules/mediasource/WebKitSourceBufferList.cpp
index 43d93d00ae8e479890df42a65218aee0440de077..a0236f7f395373aa0220281348bf4b36b5134282 100644
--- a/Source/modules/mediasource/WebKitSourceBufferList.cpp
+++ b/Source/modules/mediasource/WebKitSourceBufferList.cpp
@@ -86,7 +86,7 @@ void WebKitSourceBufferList::createAndFireEvent(const AtomicString& eventName)
 {
     ASSERT(m_asyncEventQueue);
 
-    RefPtr<Event> event = Event::create(eventName);
+    RefPtrWillBeRawPtr<Event> event = Event::create(eventName);
     event->setTarget(this);
 
     m_asyncEventQueue->enqueueEvent(event.release());