[Sync] Replace typedef with using.

components/sync/model/attachments/attachment_store.h

Index: components/sync/model/attachments/attachment_store.h
diff --git a/components/sync/model/attachments/attachment_store.h b/components/sync/model/attachments/attachment_store.h
index 0a5da9088a676a41dc727aaf94f2a5f3a091c249..f302b343a88327ff5eb6b1c6777bddf839ed0668 100644
--- a/components/sync/model/attachments/attachment_store.h
+++ b/components/sync/model/attachments/attachment_store.h
@@ -57,16 +57,15 @@ class AttachmentStore {
     SYNC,
   };
 
-  typedef base::Callback<void(const Result&)> InitCallback;
-  typedef base::Callback<void(const Result&,
-                              std::unique_ptr<AttachmentMap>,
-                              std::unique_ptr<AttachmentIdList>)>
-      ReadCallback;
-  typedef base::Callback<void(const Result&)> WriteCallback;
-  typedef base::Callback<void(const Result&)> DropCallback;
-  typedef base::Callback<void(const Result&,
-                              std::unique_ptr<AttachmentMetadataList>)>
-      ReadMetadataCallback;
+  using InitCallback = base::Callback<void(const Result&)>;
+  using ReadCallback = base::Callback<void(const Result&,
+                                           std::unique_ptr<AttachmentMap>,
+                                           std::unique_ptr<AttachmentIdList>)>;
+  using WriteCallback = base::Callback<void(const Result&)>;
+  using DropCallback = base::Callback<void(const Result&)>;
+  using ReadMetadataCallback =
+      base::Callback<void(const Result&,
+                          std::unique_ptr<AttachmentMetadataList>)>;
 
   ~AttachmentStore();