downloads: add the ability to undo download removal.

content/browser/download/download_manager_impl.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 CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_MANAGER_IMPL_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_MANAGER_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 52 matching lines @@
   void Shutdown() override;
   void GetAllDownloads(DownloadVector* result) override;
   void StartDownload(
       scoped_ptr<DownloadCreateInfo> info,
       scoped_ptr<ByteStreamReader> stream,
       const DownloadUrlParameters::OnStartedCallback& on_started) override;
   int RemoveDownloadsBetween(base::Time remove_begin,
                              base::Time remove_end) override;
   int RemoveDownloads(base::Time remove_begin) override;
   int RemoveAllDownloads() override;
+  void ReviveDownload(uint32 id) override;
+  void FinalizeRemoval(uint32 id) override;
   void DownloadUrl(scoped_ptr<DownloadUrlParameters> params) override;
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
   content::DownloadItem* CreateDownloadItem(
       uint32 id,
       const base::FilePath& current_path,
       const base::FilePath& target_path,
       const std::vector<GURL>& url_chain,
       const GURL& referrer_url,
       const std::string& mime_type,
@@ skipping 97 matching lines @@
   ObserverList<Observer> observers_;
 
   // The current active browser context.
   BrowserContext* browser_context_;
 
   // Allows an embedder to control behavior. Guaranteed to outlive this object.
   DownloadManagerDelegate* delegate_;
 
   net::NetLog* net_log_;
 
+  // Removed downloads; kept alive so users can undo the removal.
+  DownloadMap removed_downloads_;
+
   base::WeakPtrFactory<DownloadManagerImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadManagerImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_MANAGER_IMPL_H_