Oilpan: ImageObserver needs to be a GC mixin.

third_party/WebKit/Source/core/fetch/ImageResource.h

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller <mueller@kde.org>
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
@@ skipping 26 matching lines @@
 class ImageResourceClient;
 class FetchRequest;
 class ResourceFetcher;
 class FloatSize;
 class Length;
 class MemoryCache;
 class SecurityOrigin;
 
 class CORE_EXPORT ImageResource final : public Resource, public ImageObserver {
     friend class MemoryCache;
-
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(ImageResource);
 public:
     using ClientType = ImageResourceClient;
 
     static ResourcePtr<ImageResource> fetch(FetchRequest&, ResourceFetcher*);
 
     ImageResource(blink::Image*);
     // Exposed for testing
     ImageResource(const ResourceRequest&, blink::Image*);
     ~ImageResource() override;
 
@@ skipping 44 matching lines @@
     bool stillNeedsLoad() const override { return !errorOccurred() && status() == Unknown && !isLoading(); }
 
     // ImageObserver
     void decodedSizeChanged(const blink::Image*, int delta) override;
     void didDraw(const blink::Image*) override;
 
     bool shouldPauseAnimation(const blink::Image*) override;
     void animationAdvanced(const blink::Image*) override;
     void changedInRect(const blink::Image*, const IntRect&) override;
 
+    DECLARE_VIRTUAL_TRACE();
+
 protected:
     bool isSafeToUnlock() const override;
     void destroyDecodedDataIfPossible() override;
     void destroyDecodedDataForFailedRevalidation() override;
 
 private:
     class ImageResourceFactory : public ResourceFactory {
     public:
         ImageResourceFactory()
             : ResourceFactory(Resource::Image) { }
@@ skipping 19 matching lines @@
 
     RefPtr<blink::Image> m_image;
     bool m_hasDevicePixelRatioHeaderValue;
 };
 
 DEFINE_RESOURCE_TYPE_CASTS(Image);
 
 }
 
 #endif