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

Source/modules/encryptedmedia/MediaKeySession.h

Index: Source/modules/encryptedmedia/MediaKeySession.h
diff --git a/Source/modules/encryptedmedia/MediaKeySession.h b/Source/modules/encryptedmedia/MediaKeySession.h
index 8881515e22b94db9737b737c24d08bbec9d7589d..50a6db1d06d5e2ca38a830cde2f515b37eabc4d3 100644
--- a/Source/modules/encryptedmedia/MediaKeySession.h
+++ b/Source/modules/encryptedmedia/MediaKeySession.h
@@ -66,7 +66,8 @@ class MediaKeys;
 class MediaKeySession FINAL
     : public RefCountedWillBeRefCountedGarbageCollected<MediaKeySession>, public ActiveDOMObject, public ScriptWrappable, public EventTargetWithInlineData
     , private blink::WebContentDecryptionModuleSession::Client {
-    DEFINE_EVENT_TARGET_REFCOUNTING(RefCountedWillBeRefCountedGarbageCollected<MediaKeySession>);
+    REFCOUNTED_EVENT_TARGET(MediaKeySession);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(MediaKeySession);
 public:
     static PassRefPtrWillBeRawPtr<MediaKeySession> create(ExecutionContext*, blink::WebContentDecryptionModule*, WeakPtrWillBeRawPtr<MediaKeys>);
     virtual ~MediaKeySession();
@@ -91,7 +92,7 @@ public:
     virtual bool hasPendingActivity() const OVERRIDE;
     virtual void stop() OVERRIDE;
 
-    void trace(Visitor*);
+    virtual void trace(Visitor*) OVERRIDE;
 
 private:
     // A struct holding the pending action.