Oilpan: make DOMWindowProperty a GC mixin.

Source/core/timing/PerformanceNavigation.cpp

 /*
  * 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:
  *
  *     * 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 60 matching lines @@
     if (!loader)
         return 0;
 
     DocumentLoadTiming* timing = loader->timing();
     if (timing->hasCrossOriginRedirect())
         return 0;
 
     return timing->redirectCount();
 }
 
+void PerformanceNavigation::trace(Visitor* visitor)
+{
+    DOMWindowProperty::trace(visitor);
+}
+
 } // namespace blink