Refactor StringPiece hash.

components/mus/ws/ids.h

 // Copyright 2014 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.
 
 #ifndef COMPONENTS_MUS_WS_IDS_H_
 #define COMPONENTS_MUS_WS_IDS_H_
 
 #include <stdint.h>
 
 #include <tuple>
 
+#include "base/containers/hash_tables.h"
 #include "base/hash.h"
 #include "components/mus/common/types.h"
 #include "components/mus/common/util.h"
 
 namespace mus {
 namespace ws {
 
 // Connection id is used to indicate no connection. That is, no WindowTreeImpl
 // ever gets this id.
 const ConnectionSpecificId kInvalidConnectionId = 0;
@@ skipping 81 matching lines @@
 template <>
 struct hash<mus::ws::WindowId> {
   size_t operator()(const mus::ws::WindowId& id) const {
     return hash<mus::Id>()(WindowIdToTransportId(id));
   }
 };
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // COMPONENTS_MUS_WS_IDS_H_