Fix JSON serialization of PerformanceEntry subclasses

third_party/WebKit/Source/core/timing/PerformanceCompositeTiming.h

 /*
  * Copyright (C) 2015 Google Inc. All rights reserved.
  * Copyright (C) 2015 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 35 matching lines @@
 public:
     static PerformanceCompositeTiming* create(Document* requestingDocument, unsigned sourceFrame, double startTime)
     {
         return new PerformanceCompositeTiming(requestingDocument, sourceFrame, startTime);
     }
 
     unsigned sourceFrame() const;
 
     DECLARE_VIRTUAL_TRACE();
 
+protected:
+    void buildJSONValue(V8ObjectBuilder&) const override;
+
 private:
     PerformanceCompositeTiming(Document* requestingDocument, unsigned sourceFrame, double startTime);
     ~PerformanceCompositeTiming() override;
 
     unsigned m_sourceFrame;
     RefPtrWillBeMember<Document> m_requestingDocument;
 };
 
 } // namespace blink
 
 #endif // PerformanceCompositeTiming_h