Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/add_unique_urls_task.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/add_unique_urls_task.h"
+
+namespace offline_pages {
+
+AddUniqueUrlsTask::AddUniqueUrlsTask(
+    PrefetchStore* store,
+    const std::string& name_space,
+    const std::vector<PrefetchURL>& prefetch_urls)
+    : store_(store),
+      name_space_(name_space),
+      prefetch_urls_(prefetch_urls),
+      weak_ptr_factory_(this) {}
+
+AddUniqueUrlsTask::~AddUniqueUrlsTask() {}
+
+void AddUniqueUrlsTask::Run() {

[dewittj, 2017/05/23 20:02:20]

Task::TaskComplete is never called?

[carlosk, 2017/05/24 20:57:26]

Done.

+  store_->CreateItemsForUniqueUrls(
+      name_space_, prefetch_urls_,
+      PrefetchStore::CreateItemsForUniqueUrlsCallback());

[dewittj, 2017/05/23 20:02:20]

This just runs a void callback, doesn't make sense to me.   Seems that the
callback should be passed in the constructor?

[carlosk, 2017/05/24 20:57:26]

Now that we need to call TaskComplete we need the callback and it should be
controlled by the task. Also this task is expected to have more steps so the
callback will eventually trigger followup work.

+}
+
+}  // namespace offline_pages