Only show Last N Pages in the UI when the corresponding tab is visible.

components/offline_pages/core/downloads/download_ui_adapter.h

 // Copyright 2016 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_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 95 matching lines @@
   // RequestCoordinator::Observer
   void OnAdded(const SavePageRequest& request) override;
   void OnCompleted(const SavePageRequest& request,
                    RequestNotifier::BackgroundSavePageResult status) override;
   void OnChanged(const SavePageRequest& request) override;
 
   // For the DownloadUIAdapter::Delegate, to report the temporary hidden status
   // change.
   void TemporaryHiddenStatusChanged(const ClientId& client_id);
 
+  Delegate* delegate() { return delegate_.get(); }
+
  private:
   enum class State { NOT_LOADED, LOADING_PAGES, LOADING_REQUESTS, LOADED };
 
   struct ItemInfo {
-    explicit ItemInfo(const OfflinePageItem& page);
-    explicit ItemInfo(const SavePageRequest& request);
+    ItemInfo(Delegate* delegate, const OfflinePageItem& page);

[Dmitry Titov, 2017/02/14 23:01:03]

It'd be nice to avoid passing a delegate simply to pull the 'temporary hidden'
bit. Rather can pass a bit.

ItmeInfo is good as a data bag, and it doesn't keep pointers to Adapter nor
Delegate, so it'd be nice to keep it this way.

[dewittj, 2017/02/15 19:49:45]

Done.

+    ItemInfo(Delegate* delegate, const SavePageRequest& request);
     ~ItemInfo();
 
     std::unique_ptr<DownloadUIItem> ui_item;
 
     // Additional cached data, not exposed to UI through DownloadUIItem.
     // Indicates if this item wraps the completed page or in-progress request.
     bool is_request;
 
     // These are shared between pages and requests.
     int64_t offline_id;
@@ skipping 19 matching lines @@
   void ClearCache();
 
   // Task callbacks.
   void OnOfflinePagesLoaded(const MultipleOfflinePageItemResult& pages);
   void OnRequestsLoaded(std::vector<std::unique_ptr<SavePageRequest>> requests);
 
   void NotifyItemsLoaded(Observer* observer);
   void OnDeletePagesDone(DeletePageResult result);
 
   void AddItemHelper(std::unique_ptr<ItemInfo> item_info);
+  // This function is not re-entrant.  It temporarily sets |deleting_item_|
+  // while it runs, so that functions such as |GetOfflineIdByGuid| will work
+  // during the |ItemDeleted| callback.
   void DeleteItemHelper(const std::string& guid);
 
   // Always valid, this class is a member of the model.
   OfflinePageModel* model_;
 
   // Always valid, a service.
   RequestCoordinator* request_coordinator_;
 
   // A delegate, supplied at construction.
   std::unique_ptr<Delegate> delegate_;
 
   State state_;
 
   // The cache of UI items. The key is DownloadUIItem.guid.
   DownloadUIItems items_;
 
+  std::unique_ptr<ItemInfo> deleting_item_;
+
   // The observers.
   base::ObserverList<Observer> observers_;
   int observers_count_;
 
   base::WeakPtrFactory<DownloadUIAdapter> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadUIAdapter);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_