sync: Implement per-type GetCommitIds

sync/engine/get_commit_ids.h

Index: sync/engine/get_commit_ids.h
diff --git a/sync/engine/get_commit_ids.h b/sync/engine/get_commit_ids.h
new file mode 100644
index 0000000000000000000000000000000000000000..9e915a94dc0e13847cc3c0e8d9551e16058315ae
--- /dev/null
+++ b/sync/engine/get_commit_ids.h
@@ -0,0 +1,56 @@
+// Copyright 2012 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 sessions {
+class OrderedCommitSet;
+}
+
+namespace syncable {
+class BaseTransaction;
+}
+
+// These functions return 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.
+//
+// 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.
+
+// Returns up to |max_entries| metahandles of entries that belong to the
+// specified |type| and are ready for commit.  The returned handles will be
+// in a valid commit ordering.
+SYNC_EXPORT_PRIVATE void GetCommitIdsForType(
+    syncable::BaseTransaction* trans,
+    ModelType type,
+    size_t max_entries,
+    std::vector<int64>* out);
+
+// Fills the specified |ordered_commit_set| with up to |commit_batch_size|
+// metahandles that belong to the set of types |requested_types| and are ready
+// for commit.  The list will be in a valid commit ordering.
+SYNC_EXPORT_PRIVATE void GetCommitIds(
+    syncable::BaseTransaction* trans,
+    ModelTypeSet requested_types,
+    size_t commit_batch_size,
+    sessions::OrderedCommitSet* ordered_commit_set);
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_GET_COMMIT_IDS_H_