Enable Oilpan for core/timing/.

Source/core/timing/DOMWindowPerformance.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DOMWindowPerformance_h
 #define DOMWindowPerformance_h
 
 #include "core/CoreExport.h"
 #include "core/frame/DOMWindowProperty.h"
 #include "platform/Supplementable.h"
@@ skipping 14 matching lines @@
     static Performance* performance(DOMWindow&);
 
     DECLARE_TRACE();
 
 private:
     explicit DOMWindowPerformance(LocalDOMWindow&);
     static const char* supplementName();
 
     Performance* performance();
 
-    LocalDOMWindow& m_window;
-    RefPtrWillBeMember<Performance> m_performance;
+    // TODO(sof): try to move this direct reference and instead rely on frame().
+    RawPtrWillBeMember<LocalDOMWindow> m_window;
+    PersistentWillBeMember<Performance> m_performance;
 };
 
 } // namespace blink
 
 #endif // DOMWindowPerformance_h