Oilpan: Move WorkerClients to the managed heap and trace its supplements.

Source/platform/Supplementable.h

 /*
  * Copyright (C) 2012 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 166 matching lines @@
         return this->m_supplements.get(key);
     }
 
     void reattachThread()
     {
 #if !ASSERT_DISABLED
         m_threadId = currentThread();
 #endif
     }
 
-    void trace(Visitor* visitor) { visitor->trace(m_supplements); }
+    virtual void trace(Visitor* visitor) { visitor->trace(m_supplements); }
 
 private:
     typename SupplementableTraits<T, isGarbageCollected>::SupplementMap m_supplements;
 
 #if !ASSERT_DISABLED
 protected:
     SupplementableBase() : m_threadId(currentThread()) { }
 
 private:
     ThreadIdentifier m_threadId;
@@ skipping 18 matching lines @@
 };
 
 template<typename T>
 struct ThreadingTrait<WebCore::SupplementableBase<T, true> > {
     static const ThreadAffinity Affinity = ThreadingTrait<T>::Affinity;
 };
 
 } // namespace WebCore
 
 #endif // Supplementable_h