Oilpan: simplify ImageLoaderClient handling.

Source/core/loader/ImageLoader.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2009 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 140 matching lines @@
 
     void willRemoveClient(ImageLoaderClient&);
 
     // For Oilpan, we must run dispose() as a prefinalizer and call
     // m_image->removeClient(this) (and more.) Otherwise, the ImageResource can invoke
     // didAddClient() for the ImageLoader that is about to die in the current
     // lazy sweeping, and the didAddClient() can access on-heap objects that
     // have already been finalized in the current lazy sweeping.
     void dispose();
 
+#if ENABLE(OILPAN)
+    void clearWeakMembers(Visitor*);
+#endif
+
     RawPtrWillBeMember<Element> m_element;
     ResourcePtr<ImageResource> m_image;
     // FIXME: Oilpan: We might be able to remove this Persistent hack when
     // ImageResourceClient is traceable.
     GC_PLUGIN_IGNORE("http://crbug.com/383741")
     RefPtrWillBePersistent<Element> m_keepAlive;
 
-#if ENABLE(OILPAN)
-    class ImageLoaderClientRemover {
-    public:
-        ImageLoaderClientRemover(ImageLoader& loader, ImageLoaderClient& client) : m_loader(loader), m_client(client) { }
-        ~ImageLoaderClientRemover();
-
-    private:
-        ImageLoader& m_loader;
-        ImageLoaderClient& m_client;
-    };
-    friend class ImageLoaderClientRemover;
-
-    // Oilpan: This ImageLoader object must outlive its clients because they
-    // need to call ImageLoader::willRemoveClient before they
-    // die. Non-Persistent HeapHashMap doesn't work well because weak processing
-    // for HeapHashMap is not triggered when both of ImageLoader and
-    // ImageLoaderClient are unreachable.
-    GC_PLUGIN_IGNORE("http://crbug.com/383742")
-    PersistentHeapHashMap<WeakMember<ImageLoaderClient>, OwnPtr<ImageLoaderClientRemover>> m_clients;
-#else
+    // Oilpan: the client references are weak, and managed as such via clearWeakMembers();
     HashSet<ImageLoaderClient*> m_clients;

[haraken, 2015/07/13 14:46:56]

I'm wondering if we could just use HeapHashSet<WeakMember<ImageLoaderClient>>
but doesn't it work for some reason?

[sof, 2015/07/13 14:49:44]

We need to explicitly unregister (==willRemoveClient()) upon them falling away,
so a custom weak callback is needed.

This representation mirrors how LocalFrame::m_pluginElements are kept.

-#endif
     Timer<ImageLoader> m_derefElementTimer;
     AtomicString m_failedLoadURL;
     WeakPtr<Task> m_pendingTask; // owned by Microtask
     OwnPtr<IncrementLoadEventDelayCount> m_loadDelayCounter;
     bool m_hasPendingLoadEvent : 1;
     bool m_hasPendingErrorEvent : 1;
     bool m_imageComplete : 1;
     bool m_loadingImageDocument : 1;
     bool m_elementIsProtected : 1;
     bool m_suppressErrorEvents : 1;
     unsigned m_highPriorityClientCount;
 };
 
 }
 
 #endif