[Sync] Replace typedef with using.

components/sync/test/fake_server/sessions_hierarchy.h

 // Copyright 2015 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_SYNC_TEST_FAKE_SERVER_SESSIONS_HIERARCHY_H_
 #define COMPONENTS_SYNC_TEST_FAKE_SERVER_SESSIONS_HIERARCHY_H_
 
 #include <set>
 #include <string>
 
@@ skipping 29 matching lines @@
   //    (and vice versa).
   //
   // Examples of equivalent hierarchies:
   //   {} and {}, {{X}} and {{X}}, {{X,Y}} and {{Y,X}}, {{X},{Y}} and {{Y},{X}}
   // Examples of nonequivalent hierarchies:
   //   {{X}} and {{Y}}, {{X}} and {{X,X}}, {{X}} and {{X},{X}}
   bool Equals(const SessionsHierarchy& other) const;
 
  private:
   // A collection of tab URLs.
-  typedef std::multiset<std::string> Window;
+  using Window = std::multiset<std::string>;
 
   // A collection of Windows (an instance of this collection represents a
   // sessions hierarchy).
-  typedef std::multiset<Window> WindowContainer;
+  using WindowContainer = std::multiset<Window>;
 
   // The windows of the sessions hierarchy.
   WindowContainer windows_;
 };
 
 }  // namespace fake_server
 
 #endif  // COMPONENTS_SYNC_TEST_FAKE_SERVER_SESSIONS_HIERARCHY_H_