Add a Model to the download component.

components/download/internal/noop_store.h

Index: components/download/internal/noop_store.h
diff --git a/components/download/internal/noop_store.h b/components/download/internal/noop_store.h
new file mode 100644
index 0000000000000000000000000000000000000000..32d1be58bc39151df8ee9a1d3cf8cab646124c32
--- /dev/null
+++ b/components/download/internal/noop_store.h
@@ -0,0 +1,44 @@
+// 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_DOWNLOAD_INTERNAL_NOOP_STORE_H_
+#define COMPONENTS_DOWNLOAD_INTERNAL_NOOP_STORE_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/download/internal/store.h"
+
+namespace download {
+
+struct Entry;
+
+// A Store implementation that doesn't do anything but honors the interface
+// requirements.

[Peter Beverloo, 2017/05/10 12:44:45]

Once an actual ProtoDB store is in place, will this class be removed in favor of
store_impl? Might be worth adding a TODO for that.

[David Trainor- moved to gerrit, 2017/05/15 15:59:52]

I was going to leave it for tests.  Will add a TODO to track what should happen
to it though.

+class NoopStore : public Store {
+ public:
+  NoopStore();
+  ~NoopStore() override;
+
+  // Store implementation.
+  bool IsInitialized() override;
+  void Initialize(const InitCallback& callback) override;
+  void Destroy(const StoreCallback& callback) override;
+  void Update(const Entry& entry, const StoreCallback& callback) override;
+  void Remove(const std::string& guid, const StoreCallback& callback) override;
+
+ private:
+  void OnInitFinished(const InitCallback& callback);
+
+  // Whether or not this Store is 'initialized.'  Just gets set to |true| once
+  // Initialize() is called.
+  bool initialized_;
+
+  base::WeakPtrFactory<NoopStore> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(NoopStore);
+};
+
+}  // namespace download
+
+#endif  // COMPONENTS_DOWNLOAD_INTERNAL_NOOP_STORE_H_