[Sync] Replace typedef with using.

components/sync/base/immutable.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_BASE_IMMUTABLE_H_
 #define COMPONENTS_SYNC_BASE_IMMUTABLE_H_
 
 #include <utility>
 
 #include "base/macros.h"
@@ skipping 169 matching lines @@
 //     delete *wrapper;
 //   }
 //
 //   ...
 //
 // Also note that this incurs an additional memory allocation when you
 // create an Immutable<SomeOtherType>.
 
 template <typename T>
 struct DefaultImmutableTraits {
-  typedef T Wrapper;
+  using Wrapper = T;
 
   static void InitializeWrapper(Wrapper* wrapper) {}
 
   static void DestroyWrapper(Wrapper* wrapper) {}
 
   static const T& Unwrap(const Wrapper& wrapper) { return wrapper; }
 
   static T* UnwrapMutable(Wrapper* wrapper) { return wrapper; }
 
   static void Swap(T* t1, T* t2) {
@@ skipping 37 matching lines @@
 
 // Helper function to avoid having to write out template arguments.
 template <typename T>
 Immutable<T> MakeImmutable(T* t) {
   return Immutable<T>(t);
 }
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_BASE_IMMUTABLE_H_