Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/add_unique_urls_task.cc

Index: components/offline_pages/core/prefetch/add_unique_urls_task.cc
diff --git a/components/offline_pages/core/prefetch/add_unique_urls_task.cc b/components/offline_pages/core/prefetch/add_unique_urls_task.cc
new file mode 100644
index 0000000000000000000000000000000000000000..58f46a0ed03a00df250c1276d8ed5439ac2aeef2
--- /dev/null
+++ b/components/offline_pages/core/prefetch/add_unique_urls_task.cc
@@ -0,0 +1,25 @@
+// 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::vector<PrefetchURL>& prefetch_urls)
+    : prefetch_store_(store),
+      prefetch_urls_(prefetch_urls),
+      weak_ptr_factory_(this) {}
+
+AddUniqueUrlsTask::~AddUniqueUrlsTask() {}
+
+void AddUniqueUrlsTask::Run() {
+  CHECK(prefetch_store_);
+  TaskComplete();
+}
+
+}  // namespace offline_pages