Add a Model to the download component.

components/download/internal/model_impl.h

Index: components/download/internal/model_impl.h
diff --git a/components/download/internal/model_impl.h b/components/download/internal/model_impl.h
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+++ b/components/download/internal/model_impl.h
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+// Copyright 2017 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_DOWNLOAD_INTERNAL_MODEL_IMPL_H_
+#define COMPONENTS_DOWNLOAD_INTERNAL_MODEL_IMPL_H_
+
+#include <map>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/download/internal/model.h"
+#include "components/download/internal/store.h"
+#include "components/download/public/clients.h"
+
+namespace download {
+
+struct Entry;
+
+// The internal implementation of Model.
+class ModelImpl : public Model {
+ public:
+  ModelImpl(Client* client, std::unique_ptr<Store> store);
+  ~ModelImpl() override;
+
+  // Model implementation.
+  void Initialize() override;
+  void Destroy() override;
+  void Add(const Entry& entry) override;
+  void Update(const Entry& entry) override;
+  void Remove(const std::string& guid) override;
+  Entry* Get(const std::string& guid) override;
+  EntryList PeekEntries() override;
+
+ private:
+  using OwnedEntryMap = std::map<std::string, std::unique_ptr<Entry>>;
+
+  void OnInitializedFinished(bool success,
+                             std::unique_ptr<std::vector<Entry>> entries);
+  void OnDestroyFinished(bool success);
+  void OnAddFinished(DownloadClient client,
+                     const std::string& guid,
+                     bool success);
+  void OnUpdateFinished(DownloadClient client,
+                        const std::string& guid,
+                        bool success);
+  void OnRemoveFinished(DownloadClient client,
+                        const std::string& guid,
+                        bool success);
+
+  // The external Model::Client reference that will receive all interesting
+  // Model notifications.
+  Client* const client_;
+
+  // The backing Store that is responsible for saving and loading the
+  // persisted entries.
+  std::unique_ptr<Store> store_;
+
+  // A map of [guid] -> [std::unique_ptr<Entry>].  Effectively the cache of the
+  // entries saved in Store.
+  OwnedEntryMap entries_;
+
+  base::WeakPtrFactory<ModelImpl> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ModelImpl);
+};
+
+}  // namespace download
+
+#endif  // COMPONENTS_DOWNLOAD_INTERNAL_MODEL_IMPL_H_