[Sync] Replace typedef with using.

components/sync/js/js_event_details.h

 // Copyright 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_JS_JS_EVENT_DETAILS_H_
 #define COMPONENTS_SYNC_JS_JS_EVENT_DETAILS_H_
 
 // See README.js for design comments.
 
 #include <string>
@@ skipping 17 matching lines @@
 
   ~JsEventDetails();
 
   const base::DictionaryValue& Get() const;
 
   std::string ToString() const;
 
   // Copy constructor and assignment operator welcome.
 
  private:
-  typedef Immutable<base::DictionaryValue,
-                    HasSwapMemFnByPtr<base::DictionaryValue>>
-      ImmutableDictionaryValue;
+  using ImmutableDictionaryValue =
+      Immutable<base::DictionaryValue,
+                HasSwapMemFnByPtr<base::DictionaryValue>>;
 
   ImmutableDictionaryValue details_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_JS_JS_EVENT_DETAILS_H_