Add [WillBeGarbageCollected] to Event.idl

Source/core/events/MessageEvent.cpp

Index: Source/core/events/MessageEvent.cpp
diff --git a/Source/core/events/MessageEvent.cpp b/Source/core/events/MessageEvent.cpp
index da5c947fd0dc82b1bc02dee5e37d9146cefc9e80..3bc8a3d50e56d69b95b06e1f94669787201df95d 100644
--- a/Source/core/events/MessageEvent.cpp
+++ b/Source/core/events/MessageEvent.cpp
@@ -133,13 +133,13 @@ MessageEvent::~MessageEvent()
 {
 }
 
-PassRefPtr<MessageEvent> MessageEvent::create(const AtomicString& type, const MessageEventInit& initializer, ExceptionState& exceptionState)
+PassRefPtrWillBeRawPtr<MessageEvent> MessageEvent::create(const AtomicString& type, const MessageEventInit& initializer, ExceptionState& exceptionState)
 {
     if (initializer.source.get() && !isValidSource(initializer.source.get())) {
         exceptionState.throwTypeError("The optional 'source' property is neither a Window nor MessagePort.");
         return nullptr;
     }
-    return adoptRef(new MessageEvent(type, initializer));
+    return adoptRefWillBeRefCountedGarbageCollected(new MessageEvent(type, initializer));
 }
 
 void MessageEvent::initMessageEvent(const AtomicString& type, bool canBubble, bool cancelable, const String& origin, const String& lastEventId, DOMWindow* source, PassOwnPtr<MessagePortArray> ports)