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

Source/core/dom/NodeListsNodeData.cpp

 /*
  * 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:
  *
  *     * 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 31 matching lines @@
     if (attrName)
         return;
 
     TagCollectionCacheNS::iterator tagCacheEnd = m_tagCollectionCacheNS.end();
     for (TagCollectionCacheNS::iterator it = m_tagCollectionCacheNS.begin(); it != tagCacheEnd; ++it)
         it->value->invalidateCache();
 }
 
 void NodeListsNodeData::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_childNodeList);
     visitor->trace(m_atomicNameCaches);
     visitor->trace(m_tagCollectionCacheNS);
+#endif
 }
 
 } // namespace blink