Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_test_store.cc

+// 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.
+
+#include "components/offline_pages/core/prefetch/prefetch_test_store.h"
+
+namespace offline_pages {
+
+void PrefetchTestStore::CreateItemsForUniqueUrls(
+    const std::string& name_space,
+    const std::vector<PrefetchURL>& prefetch_urls,
+    const PrefetchStore::CreateItemsForUniqueUrlsCallback& callback) {
+  NOTIMPLEMENTED();
+}
+
+void PrefetchTestStore::Reset(const PrefetchStore::ResetCallback& callback) {
+  NOTIMPLEMENTED();
+}
+
+}  // namespace offline_pages