[Sync] use base::Time in sync

chrome/browser/sync/syncable/syncable_columns.h

Index: chrome/browser/sync/syncable/syncable_columns.h
diff --git a/chrome/browser/sync/syncable/syncable_columns.h b/chrome/browser/sync/syncable/syncable_columns.h
index 94bd0acb6a4d7b196ec7a6e7e5406e06ed05260f..185d510b545bf22e5589239233f7e3a60350d5f4 100644
--- a/chrome/browser/sync/syncable/syncable_columns.h
+++ b/chrome/browser/sync/syncable/syncable_columns.h
@@ -23,15 +23,15 @@ static const ColumnSpec g_metas_columns[] = {
   {"metahandle", "bigint primary key ON CONFLICT FAIL"},
   {"base_version", "bigint default " CHANGES_VERSION_STRING},
   {"server_version", "bigint default 0"},
-  // These timestamps are kept in native file timestamp format.  It is
-  // up to the syncer to translate to Java time when syncing.
+  {"server_position_in_parent", "bigint default 0"},
+  // This is the item ID that we store for the embedding application.
+  {"local_external_id", "bigint default 0"},
+  // These timestamps are kept in the same format as that of the
+  // protocol (ms since Unix epoch).
   {"mtime", "bigint default 0"},
   {"server_mtime", "bigint default 0"},
   {"ctime", "bigint default 0"},
   {"server_ctime", "bigint default 0"},
-  {"server_position_in_parent", "bigint default 0"},
-  // This is the item ID that we store for the embedding application.
-  {"local_external_id", "bigint default 0"},
   //////////////////////////////////////
   // Ids
   {"id", "varchar(255) default \"r\""},