Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_item.h

 // 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_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_ITEM_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_ITEM_H_
 
 #include <string>
 
 #include "base/time/time.h"
+#include "components/offline_pages/core/client_id.h"
 #include "components/offline_pages/core/prefetch/prefetch_types.h"
 #include "url/gurl.h"
 
 namespace offline_pages {
 
 // Data object representing an item progressing through the prefetching process
 // from the moment a URL is requested by a client until its processing is done,
 // successfully or not.
 // Instances of this class are in-memory representations of items in (or to be
 // inserted into) the persistent prefetching data store.
 struct PrefetchItem {
   PrefetchItem();
   explicit PrefetchItem(const PrefetchItem& other);
 
   ~PrefetchItem();
 
   bool operator==(const PrefetchItem& other) const;
   bool operator!=(const PrefetchItem& other) const;
 
   // Primary key/ID for this prefetch item (See |base::GenerateGUID()|). This
   // value will be reused when communicating with other systems accepting GUID
   // identifiers for operations linked to this item.
   std::string guid;
 
-  // Externally provided namespace and id values so that this item can be
-  // uniquely identified by the client requesting it. It is the client's
-  // responsibility to make sure the id is unique within the context of its
-  // assigned namespace.
-  std::string client_name_space;
-  std::string client_id;
+  // Data composed of a namespace and an uid values to allow this item to be
+  // uniquely identified by the client that requested it.
+  ClientId client_id;
 
   // Current prefetching progress state.
   PrefetchItemState state = PrefetchItemState::NEW_REQUEST;
 
   // The URL of the page the client requested to be prefetched.
   GURL url;
 
   // The final URL whose page was actually included in a successfully created
   // archive after redirects, if it was different than the |url|. It will be
   // left empty if they are the same.
@@ skipping 32 matching lines @@
   base::Time freshness_time;
 
   // The reason why the item was set to the FINISHED state. Should be
   // disregarded until reaching that state.
   PrefetchItemErrorCode error_code = PrefetchItemErrorCode::SUCCESS;
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_ITEM_H_