sync: Add interfaces for per-type sync

sync/engine/sync_directory_commit_contributor.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_SYNC_DIRECTORY_COMMIT_CONTRIBUTOR_H_
-#define SYNC_ENGINE_SYNC_DIRECTORY_COMMIT_CONTRIBUTOR_H_
-
-#include <map>
-
-#include "sync/internal_api/public/base/model_type.h"
-
-namespace syncer {
-
-class SyncDirectoryCommitContribution;
-
-namespace syncable {
-class Directory;
-}
-
-// This class represents the syncable::Directory as a source of items to commit
-// to the sync server.
-//
-// Each instance of this class represents a particular type within the
-// syncable::Directory.  When asked, it will iterate through the directory, grab
-// any items of its type that are ready for commit, and return them in the form
-// of a SyncDirectoryCommitContribution.
-class SyncDirectoryCommitContributor {
- public:
-  SyncDirectoryCommitContributor(syncable::Directory* dir, ModelType type);
-  ~SyncDirectoryCommitContributor();
-
-  SyncDirectoryCommitContribution* GetContribution(size_t max_entries);
-
- private:
-  syncable::Directory* dir_;
-  ModelType type_;
-};
-
-}  // namespace
-
-#endif  // SYNC_ENGINE_SYNC_DIRECTORY_COMMIT_CONTRIBUTOR_H_