Oilpan: ImageObserver needs to be a GC mixin.

third_party/WebKit/Source/platform/graphics/ImageObserver.h

 /*
  * Copyright (C) 2004, 2005, 2006 Apple Computer, 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
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef ImageObserver_h
 #define ImageObserver_h
 
 #include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Image;
 class IntRect;
 
 // Interface for notification about changes to an image, including decoding,
 // drawing, and animating.
-class PLATFORM_EXPORT ImageObserver {
+class PLATFORM_EXPORT ImageObserver : public WillBeGarbageCollectedMixin {
 protected:
     virtual ~ImageObserver();
 public:
     virtual void decodedSizeChanged(const Image*, int delta) = 0;
     virtual void didDraw(const Image*) = 0;
 
     virtual bool shouldPauseAnimation(const Image*) = 0;
     virtual void animationAdvanced(const Image*) = 0;
 
     virtual void changedInRect(const Image*, const IntRect&) = 0;
+
+    DEFINE_INLINE_VIRTUAL_TRACE() { }
 };
 
 } // namespace blink
 
 #endif