Add base persistence interfaces for Prefetching Offline Pages.

components/offline_pages/core/prefetch/prefetch_item.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/prefetch_item.h"
+
+namespace offline_pages {
+
+bool PrefetchItem::operator==(const PrefetchItem& other) const {
+  return id == other.id && client_id == other.client_id &&
+         state == other.state && url == other.url &&
+         final_archived_url == other.final_archived_url &&
+         request_archive_attempt_count == other.request_archive_attempt_count &&
+         operation_name == other.operation_name &&
+         archive_body_name == other.archive_body_name &&
+         archive_body_length == other.archive_body_length &&
+         download_id == other.download_id &&
+         creation_time == other.creation_time &&
+         freshness_time == other.freshness_time &&
+         error_code == other.error_code;
+}
+
+}  // namespace offline_pages