Oilpan:Allow custom handling of classes that contain weak pointers that are embedded in collections.

Source/wtf/ListHashSet.h

 /*
  * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011, Benjamin Poulain <ikipou@gmail.com>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 978 matching lines @@
         if (!m_head)
             return;
 
         for (Node* node = m_head, *next = m_head->next(); node; node = next, next = node ? node->next() : 0)
             node->destroy(this->allocator());
     }
 
     template<typename T, size_t inlineCapacity, typename U, typename V>
     void ListHashSet<T, inlineCapacity, U, V>::trace(typename Allocator::Visitor* visitor)
     {
+        COMPILE_ASSERT(HashTraits<T>::weakHandlingFlag == NoWeakHandlingInCollections, ListHashSetDoesNotSupportWeakness);
         // This marks all the nodes and their contents live that can be
         // accessed through the HashTable.
         m_impl.trace(visitor);
         // Due to the order in which entries are added to the hash table vs.
         // when they are put in the linked list we have now marked all the
         // nodes live.
         ASSERT(!m_head || Allocator::isAlive(visitor, m_head));
         ASSERT(!m_tail || Allocator::isAlive(visitor, m_tail));
     }
 
 } // namespace WTF
 
 using WTF::ListHashSet;
 
 #endif /* WTF_ListHashSet_h */