Add a Model to the download component.

components/download/internal/store.h

+// 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_STORE_H_
+#define COMPONENTS_DOWNLOAD_INTERNAL_STORE_H_
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "base/callback_forward.h"
+#include "base/memory/ref_counted.h"
+#include "base/sequenced_task_runner.h"
+
+namespace download {
+
+struct Entry;
+
+// A backing storage interface responsible for persisting Entry objects.
+class Store {
+ public:
+  using InitCallback =
+      base::Callback<void(bool success,
+                          std::unique_ptr<std::vector<Entry>> entries)>;
+  using StoreCallback = base::Callback<void(bool success)>;

[Peter Beverloo, 2017/05/10 12:44:45]

nit: these can be base::OnceCallback, allowing you to drop const& in the usage
below and use move semantics.

[David Trainor- moved to gerrit, 2017/05/15 15:59:52]

Done.

+
+  virtual ~Store() = default;
+
+  // Returns whether or not this Store is initialized and can be interracted
+  // with.
+  virtual bool IsInitialized() = 0;
+
+  // Initializes this Store and asynchronously returns whether or not that
+  // initialization was successful as well as a list of Entry objects from the
+  // Store.
+  virtual void Initialize(const InitCallback& callback) = 0;
+
+  // Destroyes the store and asynchronously returns whether or not that
+  // destruction was successful.
+  virtual void Destroy(const StoreCallback& callback) = 0;
+
+  // Adds or updates |entry| in this Store asynchronously and returns whether or
+  // not that was successful.
+  virtual void Update(const Entry& entry, const StoreCallback& callback) = 0;
+
+  // Removes the Entry associated with |guid| from this Store asynchronously and
+  // returns whether or not that was successful.
+  virtual void Remove(const std::string& guid,
+                      const StoreCallback& callback) = 0;
+};
+
+}  // namespace download
+
+#endif  // COMPONENTS_DOWNLOAD_INTERNAL_STORE_H_