Oilpan: reliably track listening PlatformEventControllers.

Source/core/frame/DeviceSingleWindowEventController.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DeviceSingleWindowEventController_h
 #define DeviceSingleWindowEventController_h
 
 #include "core/frame/DOMWindowLifecycleObserver.h"
 #include "core/frame/PlatformEventController.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Document;
 class Event;
 
 class DeviceSingleWindowEventController : public NoBaseWillBeGarbageCollectedFinalized<DeviceSingleWindowEventController>, public PlatformEventController, public DOMWindowLifecycleObserver {
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(DeviceSingleWindowEventController);
 public:
     virtual ~DeviceSingleWindowEventController();
 
     // Inherited from DeviceEventControllerBase.
     virtual void didUpdateData() OVERRIDE;
     virtual void trace(Visitor*);
 
     // Inherited from DOMWindowLifecycleObserver.
     virtual void didAddEventListener(LocalDOMWindow*, const AtomicString&) OVERRIDE;
     virtual void didRemoveEventListener(LocalDOMWindow*, const AtomicString&) OVERRIDE;
@@ skipping 11 matching lines @@
 private:
     Document& document() const { return *m_document; }
 
     bool m_needsCheckingNullEvents;
     RawPtrWillBeMember<Document> m_document;
 };
 
 } // namespace blink
 
 #endif // DeviceSingleWindowEventController_h