[Sync] Replace typedef with using.

components/sync_sessions/tab_node_pool.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_SYNC_SESSIONS_TAB_NODE_POOL_H_
 #define COMPONENTS_SYNC_SESSIONS_TAB_NODE_POOL_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 107 matching lines @@
   // Return empty status (all tab nodes are in use).
   bool Empty() const;
 
   // Return full status (no tab nodes are in use).
   bool Full();
 
   void SetMachineTag(const std::string& machine_tag);
 
  private:
   friend class SyncTabNodePoolTest;
-  typedef std::map<int, SessionID::id_type> TabNodeIDToTabIDMap;
+  using TabNodeIDToTabIDMap = std::map<int, SessionID::id_type>;
 
   // Adds |tab_node_id| to free node pool.
   // |change_output| *must* be provided. It is the TabNodePool's link to
   // the SyncChange pipeline that exists in the caller's context.
   // See FreeTabNode for more detail.
   void FreeTabNodeInternal(int tab_node_id,
                            syncer::SyncChangeList* change_output);
 
   // Stores mapping of node ids associated with tab_ids, these are the used
   // nodes of tab node pool.
@@ skipping 16 matching lines @@
   // The machine tag associated with this tab pool. Used in the title of new
   // sync nodes.
   std::string machine_tag_;
 
   DISALLOW_COPY_AND_ASSIGN(TabNodePool);
 };
 
 }  // namespace sync_sessions
 
 #endif  // COMPONENTS_SYNC_SESSIONS_TAB_NODE_POOL_H_