blink: Cleanup class/struct forward declarations

third_party/WebKit/Source/wtf/HashTraits.h

 /*
  * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 401 matching lines @@
 template <typename Key, typename Value>
 struct HashTraits<KeyValuePair<Key, Value>>
     : public KeyValuePairHashTraits<HashTraits<Key>, HashTraits<Value>> {};
 
 template <typename T>
 struct NullableHashTraits : public HashTraits<T> {
   static const bool emptyValueIsZero = false;
   static T emptyValue() { return reinterpret_cast<T>(1); }
 };
 
-// This is for tracing inside collections that have special support for weak
-// pointers. The trait has a trace method which returns true if there are weak
-// pointers to things that have not (yet) been marked live. Returning true
-// indicates that the entry in the collection may yet be removed by weak
-// handling. Default implementation for non-weak types is to use the regular
-// non-weak TraceTrait. Default implementation for types with weakness is to
-// call traceInCollection on the type's trait.
-template <WeakHandlingFlag weakHandlingFlag,
-          ShouldWeakPointersBeMarkedStrongly strongify,
-          typename T,
-          typename Traits>
-struct TraceInCollectionTrait;
-
 }  // namespace WTF
 
 using WTF::HashTraits;
 using WTF::PairHashTraits;
 using WTF::NullableHashTraits;
 using WTF::SimpleClassHashTraits;
 
 #endif  // WTF_HashTraits_h