Make WebThreadedDataReceiver wrap a Blink-managed object instead.

public/platform/WebPrivatePtr.h

 /*
  * Copyright (C) 2010 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 32 matching lines @@
 
 #if INSIDE_BLINK
 enum LifetimeManagementType {
     RefCountedLifetime,
     GarbageCollectedLifetime,
     RefCountedGarbageCollectedLifetime
 };
 
 template<typename T>
 class LifetimeOf {
-    static const bool isGarbageCollected = WTF::IsSubclassOfTemplate<T, GarbageCollected>::value;
+    static const bool isGarbageCollected = WTF::IsSubclassOfTemplate<T, GarbageCollected>::value || WTF::IsSubclass<T, GarbageCollectedMixin>::value;
     static const bool isRefCountedGarbageCollected = WTF::IsSubclassOfTemplate<T, RefCountedGarbageCollected>::value;
 public:
     static const LifetimeManagementType value =
         !isGarbageCollected ? RefCountedLifetime :
         isRefCountedGarbageCollected ? RefCountedGarbageCollectedLifetime : GarbageCollectedLifetime;
 };
 
 template<typename T, LifetimeManagementType lifetime>
 class PtrStorageImpl;
 
@@ skipping 197 matching lines @@
     // Disable the copy constructor; classes that contain a WebPrivatePtr
     // should implement their copy constructor using assign().
     WebPrivatePtr(const WebPrivatePtr<T>&);
 
     void* m_storage;
 };
 
 } // namespace blink
 
 #endif