Improve DEFINE_STATIC_LOCAL()'s handling of Blink GCed objects.

third_party/WebKit/Source/core/dom/DocumentOrderedMap.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple 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 146 matching lines @@
 
 Element* DocumentOrderedMap::getElementById(const AtomicString& key, const TreeScope* scope) const
 {
     return get<keyMatchesId>(key, scope);
 }
 
 const HeapVector<Member<Element>>& DocumentOrderedMap::getAllElementsById(const AtomicString& key, const TreeScope* scope) const
 {
     ASSERT(key);
     ASSERT(scope);
-    DEFINE_STATIC_LOCAL(Persistent<HeapVector<Member<Element>>>, emptyVector, (new HeapVector<Member<Element>>()));
+    DEFINE_STATIC_LOCAL(HeapVector<Member<Element>>, emptyVector, (new HeapVector<Member<Element>>));
 
     Map::iterator it = m_map.find(key);
     if (it == m_map.end())
-        return *emptyVector;
+        return emptyVector;
 
     Member<MapEntry>& entry = it->value;
     ASSERT(entry->count);
 
     if (entry->orderedList.isEmpty()) {
         entry->orderedList.reserveCapacity(entry->count);
         for (Element* element = entry->element ? entry->element.get() : ElementTraversal::firstWithin(scope->rootNode()); entry->orderedList.size() < entry->count; element = ElementTraversal::next(*element)) {
             ASSERT(element);
             if (!keyMatchesId(key, *element))
                 continue;
@@ skipping 30 matching lines @@
 
 DEFINE_TRACE(DocumentOrderedMap::MapEntry)
 {
     visitor->trace(element);
 #if ENABLE(OILPAN)
     visitor->trace(orderedList);
 #endif
 }
 
 } // namespace blink