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"
+
+#include "base/bind.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() {
+  store_->CreateItemsForUniqueUrls(name_space_, prefetch_urls_,

[Dmitry Titov, 2017/05/26 23:05:06]

This feels like delegating the whole thing to Store... Perhaps PrefetchStore
should be less aware about semantics of this feature and give a more sql-ish
(CRUD) interface. So in this case there would be store->ReadItems(sql_string),
check for ZOMBIES etc, then store->AddItems(items) and mayeb
store->UpdateItems(vector<item>)

[carlosk, 2017/06/01 01:49:59]

From my talks with fgorski@ I think the store and task design will change
considerably from was represented here. But also this patch has already grown
large enough so I fully removed the store implementation for it, punting it to a
followup patch.

+                                   base::Bind(&AddUniqueUrlsTask::TaskComplete,
+                                              weak_ptr_factory_.GetWeakPtr()));
+}
+
+}  // namespace offline_pages