[Sync] Replace typedef with using.

components/sync/syncable/directory.h

Index: components/sync/syncable/directory.h
diff --git a/components/sync/syncable/directory.h b/components/sync/syncable/directory.h
index c50407881e0e2370d02033cd27df63875b1b552c..2911d3d562b938986eebe620836d002c7ab1cc5d 100644
--- a/components/sync/syncable/directory.h
+++ b/components/sync/syncable/directory.h
@@ -67,15 +67,15 @@ enum InvariantCheckLevel {
 // treated as pseudo-private.
 class Directory {
  public:
-  typedef std::vector<int64_t> Metahandles;
-
-  typedef std::unordered_map<int64_t, std::unique_ptr<EntryKernel>>
-      MetahandlesMap;
-  typedef std::unordered_map<std::string, EntryKernel*> IdsMap;
-  typedef std::unordered_map<std::string, EntryKernel*> TagsMap;
-  typedef std::string AttachmentIdUniqueId;
-  typedef std::unordered_map<AttachmentIdUniqueId, MetahandleSet>
-      IndexByAttachmentId;
+  using Metahandles = std::vector<int64_t>;
+
+  using MetahandlesMap =
+      std::unordered_map<int64_t, std::unique_ptr<EntryKernel>>;
+  using IdsMap = std::unordered_map<std::string, EntryKernel*>;
+  using TagsMap = std::unordered_map<std::string, EntryKernel*>;
+  using AttachmentIdUniqueId = std::string;
+  using IndexByAttachmentId =
+      std::unordered_map<AttachmentIdUniqueId, MetahandleSet>;
 
   static const base::FilePath::CharType kSyncDatabaseFilename[];