Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_test_store.cc

Index: components/offline_pages/core/prefetch/prefetch_test_store.cc
diff --git a/components/offline_pages/core/prefetch/prefetch_test_store.cc b/components/offline_pages/core/prefetch/prefetch_test_store.cc
new file mode 100644
index 0000000000000000000000000000000000000000..55056d5e69afab54fcc3436cc07b5d4ecf8b2e18
--- /dev/null
+++ b/components/offline_pages/core/prefetch/prefetch_test_store.cc
@@ -0,0 +1,17 @@
+// 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();
+  callback.Run();
+}
+
+}  // namespace offline_pages