Add [WillBeGarbageCollected] to Event.idl

Source/modules/serviceworkers/FetchEvent.h

Index: Source/modules/serviceworkers/FetchEvent.h
diff --git a/Source/modules/serviceworkers/FetchEvent.h b/Source/modules/serviceworkers/FetchEvent.h
index 5f5bccf7c30b92fafbe9ead121a8c9bc37fd9e64..cca053690d60349d62c43d2f55f79e1f2dadbb95 100644
--- a/Source/modules/serviceworkers/FetchEvent.h
+++ b/Source/modules/serviceworkers/FetchEvent.h
@@ -18,14 +18,16 @@ class RespondWithObserver;
 // service worker's response.
 class FetchEvent FINAL : public Event {
 public:
-    static PassRefPtr<FetchEvent> create();
-    static PassRefPtr<FetchEvent> create(PassRefPtr<RespondWithObserver>);
+    static PassRefPtrWillBeRawPtr<FetchEvent> create();
+    static PassRefPtrWillBeRawPtr<FetchEvent> create(PassRefPtr<RespondWithObserver>);
     virtual ~FetchEvent() { }
 
     void respondWith(const ScriptValue&);
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 protected:
     FetchEvent();
     explicit FetchEvent(PassRefPtr<RespondWithObserver>);