Oilpan: ImageObserver needs to be a GC mixin.

third_party/WebKit/Source/core/svg/graphics/SVGImage.h

 /*
  * Copyright (C) 2006 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Apple 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
@@ skipping 118 matching lines @@
         m_observer = m_image->imageObserver();
         m_image->setImageObserver(0);
     }
 
     ~ImageObserverDisabler()
     {
         m_image->setImageObserver(m_observer);
     }
 private:
     Image* m_image;
-    ImageObserver* m_observer;
+    RawPtrWillBeMember<ImageObserver> m_observer;
 };
 
 } // namespace blink
 
 #endif // SVGImage_h