[Sync] Move some things from core/ to model(_impl)/.

components/sync/core/data_batch_impl.h

-// Copyright 2015 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 COMPONENTS_SYNC_CORE_DATA_BATCH_IMPL_H_
-#define COMPONENTS_SYNC_CORE_DATA_BATCH_IMPL_H_
-
-#include <stddef.h>
-
-#include <memory>
-#include <string>
-#include <utility>
-#include <vector>
-
-#include "base/macros.h"
-#include "components/sync/model/data_batch.h"
-#include "components/sync/model/entity_data.h"
-
-namespace syncer {
-
-// An implementation of DataBatch that's purpose is to transfer ownership of
-// EntityData objects. As soon as this batch recieves the EntityData, it owns
-// them until Next() is invoked, when it gives up ownerhsip. Because a vector
-// is used internally, this impl is unaware when duplcate storage_keys are used,
-// and it is the caller's job to avoid this.
-class DataBatchImpl : public DataBatch {
- public:
-  DataBatchImpl();
-  ~DataBatchImpl() override;
-
-  // Takes ownership of the data tied to a given key used for storage. Put
-  // should be called at most once for any given storfage_key. Data will be
-  // readable in the same order that they are put into the batch.
-  void Put(const std::string& storage_key,
-           std::unique_ptr<EntityData> entity_data);
-
-  // DataBatch implementation.
-  bool HasNext() const override;
-  KeyAndData Next() override;
-
- private:
-  std::vector<KeyAndData> key_data_pairs_;
-  size_t read_index_ = 0;
-
-  DISALLOW_COPY_AND_ASSIGN(DataBatchImpl);
-};
-
-}  // namespace syncer
-
-#endif  // COMPONENTS_SYNC_CORE_DATA_BATCH_IMPL_H_