Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_in_memory_store.h

Index: components/offline_pages/core/prefetch/prefetch_in_memory_store.h
diff --git a/components/offline_pages/core/prefetch/prefetch_in_memory_store.h b/components/offline_pages/core/prefetch/prefetch_in_memory_store.h
new file mode 100644
index 0000000000000000000000000000000000000000..700b3a8c0d6599a76cfd355679d5fcfdbd624396
--- /dev/null
+++ b/components/offline_pages/core/prefetch/prefetch_in_memory_store.h
@@ -0,0 +1,21 @@
+// 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_IN_MEMORY_STORE_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_IN_MEMORY_STORE_H_
+
+#include "components/offline_pages/core/prefetch/prefetch_store.h"
+
+namespace offline_pages {
+
+// A PrefetchStore implementation that keeps all persisted data in memory.
+class PrefetchInMemoryStore : public PrefetchStore {
+ public:
+  PrefetchInMemoryStore();
+  ~PrefetchInMemoryStore() override;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_IN_MEMORY_STORE_H_