[Sync] Replace typedef with using.

components/sync/engine_impl/commit.h

 // Copyright (c) 2012 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_ENGINE_IMPL_COMMIT_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_COMMIT_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 18 matching lines @@
 // This class wraps the actions related to building and executing a single
 // commit operation.
 //
 // This class' most important responsibility is to manage the ContributionsMap.
 // This class serves as a container for those objects.  Although it would have
 // been acceptable to let this class be a dumb container object, it turns out
 // that there was no other convenient place to put the Init() and
 // PostAndProcessCommitResponse() functions.  So they ended up here.
 class Commit {
  public:
-  typedef std::map<ModelType, std::unique_ptr<CommitContribution>>
-      ContributionMap;
+  using ContributionMap =
+      std::map<ModelType, std::unique_ptr<CommitContribution>>;
 
   Commit(ContributionMap contributions,
          const sync_pb::ClientToServerMessage& message,
          ExtensionsActivity::Records extensions_activity_buffer);
 
   // This destructor will DCHECK if CleanUp() has not been called.
   ~Commit();
 
   // |extensions_activity| may be null.
   static Commit* Init(ModelTypeSet requested_types,
@@ skipping 25 matching lines @@
 
   // Debug only flag used to indicate if it's safe to destruct the object.
   bool cleaned_up_;
 
   DISALLOW_COPY_AND_ASSIGN(Commit);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_COMMIT_H_