Revert of [oilpan]: Remove support for tracing off-heap hashmaps.

Source/modules/indexeddb/IDBPendingTransactionMonitor.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:
  *
  * 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
@@ skipping 23 matching lines @@
 namespace blink {
 
 class ExecutionContext;
 class IDBTransaction;
 
 // This class keeps track of the transactions created during the current
 // Javascript execution context. Transactions have an internal |active| flag
 // which is set to true on creation, but must be set to false when control
 // returns to the event loop.
 
-class IDBPendingTransactionMonitor : public NoBaseWillBeGarbageCollected<IDBPendingTransactionMonitor>, public WillBeHeapSupplement<ExecutionContext> {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(IDBPendingTransactionMonitor);
-    DECLARE_EMPTY_VIRTUAL_DESTRUCTOR_WILL_BE_REMOVED(IDBPendingTransactionMonitor);
+class IDBPendingTransactionMonitor : public Supplement<ExecutionContext> {
     WTF_MAKE_NONCOPYABLE(IDBPendingTransactionMonitor);
 
 public:
-    static IDBPendingTransactionMonitor& from(WillBeHeapSupplementable<ExecutionContext>&);
-    virtual void trace(Visitor*) OVERRIDE;
+    static IDBPendingTransactionMonitor& from(Supplementable<ExecutionContext>&);
+    virtual ~IDBPendingTransactionMonitor();
+    // The trace functino doesn't work until ExecutionContext is moved to Oilpan
+    // heap.
+    virtual void trace(Visitor* visitor) OVERRIDE { Supplement<ExecutionContext>::trace(visitor); }
     void addNewTransaction(IDBTransaction&);
     void deactivateNewTransactions();
 
 private:
     IDBPendingTransactionMonitor();
     static const char* supplementName();
 
-    PersistentHeapVectorWillBeHeapVector<Member<IDBTransaction> > m_transactions;
+    typedef PersistentHeapVector<Member<IDBTransaction> > TransactionList;
+    TransactionList m_transactions;
 };
 
 } // namespace blink
 
 #endif // IDBPendingTransactionMonitor_h