downloads: add the ability to undo download removal.

chrome/browser/download/all_download_item_notifier.h

 // Copyright (c) 2012 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 CHROME_BROWSER_DOWNLOAD_ALL_DOWNLOAD_ITEM_NOTIFIER_H_
 #define CHROME_BROWSER_DOWNLOAD_ALL_DOWNLOAD_ITEM_NOTIFIER_H_
 
 #include <set>
 
 #include "content/public/browser/download_manager.h"
@@ skipping 33 matching lines @@
     virtual ~Observer() {}
 
     virtual void OnDownloadCreated(
         content::DownloadManager* manager, content::DownloadItem* item) {}
     virtual void OnDownloadUpdated(
         content::DownloadManager* manager, content::DownloadItem* item) {}
     virtual void OnDownloadOpened(
         content::DownloadManager* manager, content::DownloadItem* item) {}
     virtual void OnDownloadRemoved(
         content::DownloadManager* manager, content::DownloadItem* item) {}
+    virtual void OnDownloadRevived(
+        content::DownloadManager* manager, content::DownloadItem* item) {}
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Observer);
   };
 
   AllDownloadItemNotifier(content::DownloadManager* manager,
                           Observer* observer);
 
   ~AllDownloadItemNotifier() override;
 
   // Returns NULL if the manager has gone down.
   content::DownloadManager* GetManager() const { return manager_; }
 
  private:
   // content::DownloadManager::Observer
   void ManagerGoingDown(content::DownloadManager* manager) override;
   void OnDownloadCreated(content::DownloadManager* manager,
                          content::DownloadItem* item) override;
+  void OnDownloadRevived(content::DownloadManager* manager,
+                         content::DownloadItem* item) override;
 
   // content::DownloadItem::Observer
   void OnDownloadUpdated(content::DownloadItem* item) override;
   void OnDownloadOpened(content::DownloadItem* item) override;
   void OnDownloadRemoved(content::DownloadItem* item) override;
   void OnDownloadDestroyed(content::DownloadItem* item) override;
 
   content::DownloadManager* manager_;
   AllDownloadItemNotifier::Observer* observer_;
   std::set<content::DownloadItem*> observing_;
 
   DISALLOW_COPY_AND_ASSIGN(AllDownloadItemNotifier);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_ALL_DOWNLOAD_ITEM_NOTIFIER_H_