Refactor StringPiece hash.

net/base/linked_hash_map.h

 // Copyright (c) 2013 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.
 //
 // This is a simplistic insertion-ordered map.  It behaves similarly to an STL
 // map, but only implements a small subset of the map's methods.  Internally, we
 // just keep a map and a list going in parallel.
 //
 // This class provides no thread safety guarantees, beyond what you would
 // normally see with std::list.
 //
 // Iterators should be stable in the face of mutations, except for an
 // iterator pointing to an element that was just deleted.
 
 #ifndef UTIL_GTL_LINKED_HASH_MAP_H_
 #define UTIL_GTL_LINKED_HASH_MAP_H_
 
 #include <stddef.h>
 
 #include <list>
+#include <unordered_map>
 #include <utility>
 
-#include "base/containers/hash_tables.h"
 #include "base/logging.h"
 #include "base/macros.h"
 
 // This holds a list of pair<Key, Value> items.  This list is what gets
 // traversed, and it's iterators from this list that we return from
 // begin/end/find.
 //
 // We also keep a map<Key, list::iterator> for find.  Since std::list is a
 // doubly-linked list, the iterators should remain stable.
-template<class Key, class Value>
+template <class Key, class Value, class Hash = std::hash<Key>>
 class linked_hash_map {
  private:
   typedef std::list<std::pair<Key, Value> > ListType;
-  typedef base::hash_map<Key, typename ListType::iterator> MapType;
+  typedef std::unordered_map<Key, typename ListType::iterator, Hash> MapType;
 
  public:
   typedef typename ListType::iterator iterator;
   typedef typename ListType::reverse_iterator reverse_iterator;
   typedef typename ListType::const_iterator const_iterator;
   typedef typename ListType::const_reverse_iterator const_reverse_iterator;
   typedef typename MapType::key_type key_type;
   typedef typename ListType::value_type value_type;
   typedef typename ListType::size_type size_type;
 
@@ skipping 187 matching lines @@
 
   // The list component, used for maintaining insertion order
   ListType list_;
 
   // |map_| contains iterators to |list_|, therefore a default copy constructor
   // or copy assignment operator would result in an inconsistent state.
   DISALLOW_COPY_AND_ASSIGN(linked_hash_map);
 };
 
 #endif  // UTIL_GTL_LINKED_HASH_MAP_H_