sync: Add interfaces for per-type sync

sync/engine/commit_contribution.h

Index: sync/engine/commit_contribution.h
diff --git a/sync/engine/commit_contribution.h b/sync/engine/commit_contribution.h
new file mode 100644
index 0000000000000000000000000000000000000000..e2e910890744eea51ad7115b18b5109687c69528
--- /dev/null
+++ b/sync/engine/commit_contribution.h
@@ -0,0 +1,54 @@
+// 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_COMMIT_CONTRIBUTION_H_
+#define SYNC_ENGINE_COMMIT_CONTRIBUTION_H_
+
+#include "sync/base/sync_export.h"
+#include "sync/internal_api/public/util/syncer_error.h"
+#include "sync/protocol/sync.pb.h"
+#include "sync/sessions/status_controller.h"
+
+namespace syncer {
+
+namespace sessions {
+class StatusController;
+}  // namespace sessions
+
+// This class represents a set of items belonging to a particular data type that
+// have been selected from a CommitContributor and prepared for commit.
+//
+// This class handles the bookkeeping related to the commit of these items.
+class SYNC_EXPORT_PRIVATE CommitContribution {
+ public:
+  CommitContribution();
+  virtual ~CommitContribution() = 0;
+
+  // Serialize this contribution's entries to the given commit request |msg|.
+  //
+  // This function is not const.  It may update some state in this contribution
+  // that will be used when processing the associated commit response.  This
+  // function should not be called more than once.
+  virtual void AddToCommitMessage(sync_pb::ClientToServerMessage* msg) = 0;
+
+  // Updates this contribution's contents in accordance with the provided
+  // |response|.
+  //
+  // It is not valid to call this function unless AddToCommitMessage() was
+  // called earlier.  This function should not be called more than once.
+  virtual SyncerError ProcessCommitResponse(
+      const sync_pb::ClientToServerResponse& response,
+      sessions::StatusController* status) = 0;
+
+  // Cleans up any temproary state associated with the commit.  Must be called
+  // before destruction.
+  virtual void CleanUp() = 0;
+
+  // Returns the number of entries included in this contribution.
+  virtual size_t GetNumEntries() const = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_COMMIT_CONTRIBUTION_H_