Move FileEnumerator to its own file, do some refactoring.

sync/syncable/directory.h

 // Copyright 2013 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 SYNC_SYNCABLE_DIRECTORY_H_
 #define SYNC_SYNCABLE_DIRECTORY_H_
 
+#include <deque>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/file_util.h"
 #include "base/gtest_prod_util.h"
 #include "base/hash_tables.h"
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/util/report_unrecoverable_error_function.h"
@@ skipping 526 matching lines @@
   // are deleted in native models as well.
   scoped_ptr<DeleteJournal> delete_journal_;
 
   DISALLOW_COPY_AND_ASSIGN(Directory);
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif // SYNC_SYNCABLE_DIRECTORY_H_