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

components/sync/core/data_batch_impl.cc

-// 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.
-
-#include "components/sync/core/data_batch_impl.h"
-
-namespace syncer {
-
-DataBatchImpl::DataBatchImpl() {}
-
-DataBatchImpl::~DataBatchImpl() {}
-
-void DataBatchImpl::Put(const std::string& storage_key,
-                        std::unique_ptr<EntityData> specifics) {
-  key_data_pairs_.push_back(KeyAndData(storage_key, std::move(specifics)));
-}
-
-bool DataBatchImpl::HasNext() const {
-  return key_data_pairs_.size() > read_index_;
-}
-
-KeyAndData DataBatchImpl::Next() {
-  DCHECK(HasNext());
-  return std::move(key_data_pairs_[read_index_++]);
-}
-
-}  // namespace syncer