First version of PerformanceObserver

Source/core/timing/PerformanceMark.h

 /*
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 22 matching lines @@
 namespace blink {
 
 class PerformanceMark final : public PerformanceEntry {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PerformanceMark* create(const String& name, double startTime)
     {
         return new PerformanceMark(name, startTime);
     }
 
-    bool isMark() override { return true; }
-
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         PerformanceEntry::trace(visitor);
     }
 
 private:
     PerformanceMark(const String& name, double startTime)
         : PerformanceEntry(name, "mark", startTime, startTime) { }
 
     ~PerformanceMark() override { }
 };
 
 } // namespace blink
 
 #endif // PerformanceMark_h