Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_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_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_STORE_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_STORE_H_
+
+#include <vector>
+
+#include "base/callback.h"
+#include "components/offline_pages/core/prefetch/prefetch_item.h"
+#include "components/offline_pages/core/prefetch/prefetch_types.h"
+
+namespace offline_pages {
+
+// Persistent storage access class for prefetching offline pages data.
+class PrefetchStore {
+ public:
+  typedef base::Callback<void()> CreateItemsForUniqueUrlsCallback;
+  typedef base::Callback<void(bool /* success */)> ResetCallback;
+
+  virtual ~PrefetchStore(){};
+
+  // Asynchronously adds URLs as new items that are not yet in the prefetch
+  // store.
+  virtual void CreateItemsForUniqueUrls(
+      const std::string& name_space,
+      const std::vector<PrefetchURL>& prefetch_urls,
+      const CreateItemsForUniqueUrlsCallback& callback) = 0;
+
+  // Resets the store.

[Dmitry Titov, 2017/05/18 21:24:02]

What exactly "Resets" mean? Could you add more to the comment?

[carlosk, 2017/05/24 20:57:26]

Even better: I'll fully remove it for now as it's not being used. :)

+  virtual void Reset(const ResetCallback& callback) = 0;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_STORE_H_