sync: Remove support for hierarchy deletions

sync/engine/get_commit_ids.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_ENGINE_GET_COMMIT_IDS_H_
 #define SYNC_ENGINE_GET_COMMIT_IDS_H_
 
 #include <vector>
 
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/syncable/directory.h"
 
 using std::vector;
 
 namespace syncer {
 
 namespace syncable {
 class BaseTransaction;
 }
 
 // Returns up to |max_entries| metahandles of entries that belong to the
 // specified |type| and are ready for commit.
 //
 // This function returns handles in "commit order".  A valid commit ordering is
-// one where parents are placed before children, predecessors are placed before
-// successors, and deletes appear after creates and moves.
+// one where server-unknown items are committed parents-first, and deletions
+// are committed children-first.
 //
-// The predecessor to successor rule was implemented when we tracked positions
-// within a folder that was sensitive to such things.  The current positioning
-// system can handle receiving the elements within a folder out of order, so we
-// may be able to remove that functionality in the future.
-// See crbug.com/287938.
+// This function also enforces some position ordering constraints that are no
+// longer necessary.  We should relax those constraints.  See crbug.com/287938.
 SYNC_EXPORT_PRIVATE void GetCommitIdsForType(
     syncable::BaseTransaction* trans,
     ModelType type,
     size_t max_entries,
     std::vector<int64>* out);
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_GET_COMMIT_IDS_H_