Use OwnPtrs for heap contains cache and persistent anchor. We were leaking the HeapContainsCache.

Source/heap/Handle.h

 /*
  * Copyright (C) 2014 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 175 matching lines @@
 // A dummy Persistent handle that ensures the list of persistents is never null.
 // This removes a test from a hot path.
 class PersistentAnchor : public PersistentNode {
 public:
     void trace(Visitor* visitor)
     {
         for (PersistentNode* current = m_next; current != this; current = current->m_next)
             current->trace(visitor);
     }
 
-private:
     virtual ~PersistentAnchor()
     {
         // FIXME: oilpan: Ideally we should have no left-over persistents at this point. However currently there is a
         // large number of objects leaked when we tear down the main thread. Since some of these might contain a
         // persistent or e.g. be RefCountedGarbageCollected we cannot guarantee there are no remaining Persistents at
         // this point.
     }
+
+private:
     PersistentAnchor() : PersistentNode(TraceMethodDelegate<PersistentAnchor, &PersistentAnchor::trace>::trampoline)
     {
         m_next = this;
         m_prev = this;
     }
 
     friend class ThreadState;
 };
 
 // Persistent handles are used to store pointers into the
@@ skipping 625 matching lines @@
 };
 
 template<typename T, typename U>
 struct NeedsTracing<HashMap<T, U> > {
     static const bool value = false;
 };
 
 } // namespace WTF
 
 #endif