Oilpan: Allocate all EventTarget derived types on the manged heap.

Source/modules/notifications/Notification.h

Index: Source/modules/notifications/Notification.h
diff --git a/Source/modules/notifications/Notification.h b/Source/modules/notifications/Notification.h
index 5e5285b7ace82161ffa647bf38c9dd1afafacc82..50b7e9c747f4384b7f59dc65a27f8a65f9e5793f 100644
--- a/Source/modules/notifications/Notification.h
+++ b/Source/modules/notifications/Notification.h
@@ -50,7 +50,7 @@ class NotificationPermissionCallback;
 
 class Notification : public RefCountedGarbageCollected<Notification>, public ScriptWrappable, public ActiveDOMObject, public EventTargetWithInlineData {
     DEFINE_EVENT_TARGET_REFCOUNTING(RefCountedGarbageCollected<Notification>);
-
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(Notification);
 public:
     static Notification* create(ExecutionContext*, const String& title, const Dictionary& options);
 
@@ -91,8 +91,6 @@ public:
     virtual void stop() OVERRIDE;
     virtual bool hasPendingActivity() const OVERRIDE;
 
-    void trace(Visitor*) { }
-
 private:
     Notification(const String& title, ExecutionContext*, NotificationClient*);