Add support for OfflinePagesDownloadBridge.

components/offline_pages/downloads/download_ui_adapter.h

Index: components/offline_pages/downloads/download_ui_adapter.h
diff --git a/components/offline_pages/downloads/download_ui_adapter.h b/components/offline_pages/downloads/download_ui_adapter.h
new file mode 100644
index 0000000000000000000000000000000000000000..d942181b52b944097b0f566aae30d411b81fd926
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+++ b/components/offline_pages/downloads/download_ui_adapter.h
@@ -0,0 +1,102 @@
+// 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_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_
+#define COMPONENTS_OFFLINE_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_
+
+#include <map>
+#include <memory>
+#include <string>
+
+#include "base/observer_list.h"
+#include "components/offline_pages/downloads/download_ui_item.h"
+#include "components/offline_pages/offline_page_model.h"
+#include "components/offline_pages/offline_page_types.h"
+
+namespace offline_pages {
+
+// Key is DownloadUIItem.guid.
+typedef
+    std::map<std::string, std::unique_ptr<DownloadUIItem>> DownloadUIItemsMap;
+
+// C++ side of the UI Adapter. Mimics DownloadManager/Item/History (since we
+// share UI with Downloads).
+// An instance of this class is owned by OfflinePageModel and is shared between
+// UI components if needed. It manages the cache of DownloadUIItems, so after
+// initial load the UI components can synchronously pull the whoel list or any
+// item by its guid.
+class DownloadUIAdapter : public OfflinePageModel::Observer {
+ public:
+  // Observer, normally implemented by UI or a Bridge.
+  class Observer {
+   public:
+    // Invoked when UI items are loaded. GetAllItems/GetItem can now be used.
+    // Must be listened for in order to start getting the items.
+    // If the items are already loaded by the time observer is added, this
+    // callback will be posted right away.
+    virtual void ItemsLoaded() = 0;
+
+    // Invoked when the UI Item was added, usually as a request to download.
+    virtual void ItemAdded(const DownloadUIItem& item) = 0;
+
+    // Invoked when the UI Item was updated. Only guid of the item is guaranteed
+    // to survive the update, all other fields can change.
+    virtual void ItemUpdated(const DownloadUIItem& item) = 0;
+
+    // Invoked when the UI Item was deleted. At this point, only guid remains.
+    virtual void ItemDeleted(const std::string& guid) = 0;
+
+   protected:
+    virtual ~Observer() = default;
+  };
+
+  explicit DownloadUIAdapter(OfflinePageModel* model);
+  ~DownloadUIAdapter() override;
+
+  // This adapter is potentially shared by UI elements, each of which adds
+  // itself as an observer.
+  // When the last observer si removed, cached list of items is destroyed and
+  // next time the initial loading will take longer.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+  const DownloadUIItemsMap& GetAllItems() const;
+  // May return nullptr.
+  const DownloadUIItem* GetItem(const std::string& guid) const;
+
+  // OfflinePageModel::Observer
+  void OfflinePageModelLoaded(OfflinePageModel* model) override;
+  void OfflinePageModelChanged(OfflinePageModel* model) override;
+  void OfflinePageDeleted(int64_t offline_id,
+                          const ClientId& client_id) override;
+
+ private:
+  void LoadCache();
+  void ClearCache();
+
+  // Task callbacks.
+  void OnOfflinePagesLoaded(const MultipleOfflinePageItemResult& pages);
+  void NotifyItemsLoaded(Observer* observer);
+  void OnOfflinePagesChanged(const MultipleOfflinePageItemResult& pages);
+  bool IsVisibleInUI(const OfflinePageItem& page);
+
+  // Always valid, this class is a member of the model.
+  OfflinePageModel* model_;
+
+  bool is_loaded_;
+
+  // The cache of UI items.
+  DownloadUIItemsMap items_;
+
+  // The observers.
+  base::ObserverList<Observer> observers_;
+
+  base::WeakPtrFactory<DownloadUIAdapter> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadUIAdapter);
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_