Oilpan: keep navigation timing objects on the heap by default.

Source/core/timing/Performance.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel 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.
@@ skipping 79 matching lines @@
     void clearMeasures(const String& measureName);
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit Performance(LocalFrame*);
 
     bool isResourceTimingBufferFull();
     void addResourceTimingBuffer(PerformanceEntry*);
 
-    mutable RefPtrWillBeMember<PerformanceNavigation> m_navigation;
-    mutable RefPtrWillBeMember<PerformanceTiming> m_timing;
+    mutable Member<PerformanceNavigation> m_navigation;
+    mutable Member<PerformanceTiming> m_timing;
 
     PerformanceEntryVector m_resourceTimingBuffer;
     unsigned m_resourceTimingBufferSize;
     double m_referenceTime;
 
     Member<MemoryInfo> m_memoryInfo;
     Member<UserTiming> m_userTiming;
 };
 
 } // namespace blink
 
 #endif // Performance_h