Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_in_memory_store.cc

Index: components/offline_pages/core/prefetch/prefetch_in_memory_store.cc
diff --git a/components/offline_pages/core/prefetch/prefetch_in_memory_store.cc b/components/offline_pages/core/prefetch/prefetch_in_memory_store.cc
new file mode 100644
index 0000000000000000000000000000000000000000..efab3dba8b63090425e23927cfc8779d24a4f248
--- /dev/null
+++ b/components/offline_pages/core/prefetch/prefetch_in_memory_store.cc
@@ -0,0 +1,13 @@
+// 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_in_memory_store.h"
+
+namespace offline_pages {
+
+PrefetchInMemoryStore::PrefetchInMemoryStore() = default;
+
+PrefetchInMemoryStore::~PrefetchInMemoryStore() = default;
+
+}  // namespace offline_pages