Oilpan: add missing leftmost trace()s for GC mixins.

Source/modules/mediastream/UserMediaController.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 21 matching lines @@
     return "UserMediaController";
 }
 
 UserMediaController::UserMediaController(UserMediaClient* client)
     : m_client(client)
 {
 }
 
 DEFINE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(UserMediaController)
 
+void UserMediaController::trace(Visitor* visitor)
+{
+    WillBeHeapSupplement<LocalFrame>::trace(visitor);
+}
+
 PassOwnPtrWillBeRawPtr<UserMediaController> UserMediaController::create(UserMediaClient* client)
 {
     return adoptPtrWillBeNoop(new UserMediaController(client));
 }
 
 void provideUserMediaTo(LocalFrame& frame, UserMediaClient* client)
 {
     UserMediaController::provideTo(frame, UserMediaController::supplementName(), UserMediaController::create(client));
 }
 
 } // namespace blink