Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_test_store.h

Index: components/offline_pages/core/prefetch/prefetch_test_store.h
diff --git a/components/offline_pages/core/prefetch/prefetch_test_store.h b/components/offline_pages/core/prefetch/prefetch_test_store.h
new file mode 100644
index 0000000000000000000000000000000000000000..272875b6a230fd25aab6d2e61ee6aab1d4a2f89f
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+++ b/components/offline_pages/core/prefetch/prefetch_test_store.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_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TEST_STORE_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TEST_STORE_H_
+
+#include "components/offline_pages/core/prefetch/prefetch_store.h"
+
+namespace offline_pages {
+
+// A PrefetchStore implementation that keeps all stored data in memory.
+class PrefetchTestStore : public PrefetchStore {
+ public:
+  PrefetchTestStore() = default;
+  ~PrefetchTestStore() override = default;
+
+  // PrefetchStore implementation.
+  void CreateItemsForUniqueUrls(
+      const std::string& name_space,
+      const std::vector<PrefetchURL>& prefetch_urls,
+      const PrefetchStore::CreateItemsForUniqueUrlsCallback& callback) override;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TEST_STORE_H_