sync: Add interfaces for per-type sync

sync/engine/update_handler.h

Index: sync/engine/update_handler.h
diff --git a/sync/engine/update_handler.h b/sync/engine/update_handler.h
new file mode 100644
index 0000000000000000000000000000000000000000..eb1ee4de6381968d8a75a99befc464d462d97d97
--- /dev/null
+++ b/sync/engine/update_handler.h
@@ -0,0 +1,63 @@
+// Copyright 2014 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_UPDATE_HANDLER_H_
+#define SYNC_ENGINE_UPDATE_HANDLER_H_
+
+#include <vector>
+
+#include "sync/base/sync_export.h"
+
+namespace sync_pb {
+class DataTypeProgressMarker;
+class SyncEntity;
+}
+
+typedef std::vector<const sync_pb::SyncEntity*> SyncEntityList;
+
+namespace syncer {
+
+namespace sessions {
+class StatusController;
+}
+
+class ModelSafeWorker;
+
+// This class represents an entity that can request, receive, and apply updates
+// from the sync server.
+class SYNC_EXPORT_PRIVATE UpdateHandler {
+ public:
+  UpdateHandler();
+  virtual ~UpdateHandler() = 0;
+
+  // Fills the given parameter with the stored progress marker for this type.
+  virtual void GetDownloadProgress(
+      sync_pb::DataTypeProgressMarker* progress_marker) const = 0;
+
+  // Processes the contents of a GetUpdates response message.
+  //
+  // Should be invoked with the progress marker and set of SyncEntities from a
+  // single GetUpdates response message.  The progress marker's type must match
+  // this update handler's type, and the set of SyncEntities must include all
+  // entities of this type found in the response message.
+  //
+  // In this context, "applicable_updates" means the set of updates belonging to
+  // this type.
+  virtual void ProcessGetUpdatesResponse(
+      const sync_pb::DataTypeProgressMarker& progress_marker,
+      const SyncEntityList& applicable_updates,
+      sessions::StatusController* status) = 0;
+
+  // Called at the end of a non-configure GetUpdates loop to apply any unapplied
+  // updates.
+  virtual void ApplyUpdates(sessions::StatusController* status) = 0;
+
+  // Called at the end of a configure GetUpdates loop to perform any required
+  // post-initial-download update application.
+  virtual void PassiveApplyUpdates(sessions::StatusController* status) = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_UPDATE_HANDLER_H_