Oilpan: ImageObserver needs to be a GC mixin.

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

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@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
@@ skipping 79 matching lines @@
     setLoading(false);
     setCustomAcceptHeader();
 }
 
 ImageResource::~ImageResource()
 {
     WTF_LOG(Timers, "~ImageResource %p", this);
     clearImage();
 }
 
+DEFINE_TRACE(ImageResource)
+{
+    Resource::trace(visitor);
+    ImageObserver::trace(visitor);
+}
+
 void ImageResource::load(ResourceFetcher* fetcher, const ResourceLoaderOptions& options)
 {
     if (!fetcher || fetcher->autoLoadImages())
         Resource::load(fetcher, options);
     else
         setLoading(false);
 }
 
 void ImageResource::didAddClient(ResourceClient* c)
 {
@@ skipping 161 matching lines @@
 
     if (m_response.mimeType() == "image/svg+xml") {
         m_image = SVGImage::create(this);
     } else {
         m_image = BitmapImage::create(this);
     }
 }
 
 inline void ImageResource::clearImage()
 {
+    if (!m_image)
+        return;
+
     // If our Image has an observer, it's always us so we need to clear the back pointer
     // before dropping our reference.
-    if (m_image)
-        m_image->setImageObserver(nullptr);
+    m_image->setImageObserver(nullptr);
     m_image.clear();
 }
 
 void ImageResource::appendData(const char* data, size_t length)
 {
     Resource::appendData(data, length);
     if (!loadingMultipartContent())
         updateImage(false);
 }
 
@@ skipping 161 matching lines @@
         return true;
     return !securityOrigin->taintsCanvas(response().url());
 }
 
 bool ImageResource::loadingMultipartContent() const
 {
     return m_loader && m_loader->loadingMultipartContent();
 }
 
 } // namespace blink