Clean up forward declarations in Source/core

Source/core/timing/PerformanceUserTiming.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 21 matching lines @@
 #include "wtf/HashMap.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/text/StringHash.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class ExceptionState;
 class Performance;
-class PerformanceEntry;
 
 typedef unsigned long long (PerformanceTiming::*NavigationTimingFunction)() const;
 using PerformanceEntryMap = WillBeHeapHashMap<String, PerformanceEntryVector>;
 
 class UserTiming : public RefCountedWillBeGarbageCollected<UserTiming> {
 public:
     static PassRefPtrWillBeRawPtr<UserTiming> create(Performance* performance)
     {
         return adoptRefWillBeNoop(new UserTiming(performance));
     }
@@ skipping 17 matching lines @@
 
     double findExistingMarkStartTime(const String& markName, ExceptionState&);
     RawPtrWillBeMember<Performance> m_performance;
     PerformanceEntryMap m_marksMap;
     PerformanceEntryMap m_measuresMap;
 };
 
 }
 
 #endif // !defined(PerformanceUserTiming_h)