downloads: add the ability to undo download removal.

content/public/browser/download_manager.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.
 //
 // The DownloadManager object manages the process of downloading, including
 // updates to the history system and providing the information for displaying
 // the downloads view in the Destinations tab. There is one DownloadManager per
 // active browser context in Chrome.
 //
 // Download observers:
@@ skipping 65 matching lines @@
     // A DownloadItem was created. This item may be visible before the filename
     // is determined; in this case the return value of GetTargetFileName() will
     // be null.  This method may be called an arbitrary number of times, e.g.
     // when loading history on startup.  As a result, consumers should avoid
     // doing large amounts of work in OnDownloadCreated().  TODO(<whoever>):
     // When we've fully specified the possible states of the DownloadItem in
     // download_item.h, we should remove the caveat above.
     virtual void OnDownloadCreated(
         DownloadManager* manager, DownloadItem* item) {}
 
+    // Happens when a removed item is revived (the removal is undone).
+    virtual void OnDownloadRevived(
+        DownloadManager* manager, DownloadItem* item) {}
+
     // A SavePackage has successfully finished.
     virtual void OnSavePackageSuccessfullyFinished(
         DownloadManager* manager, DownloadItem* item) {}
 
     // Called when the DownloadManager is being destroyed to prevent Observers
     // from calling back to a stale pointer.
     virtual void ManagerGoingDown(DownloadManager* manager) {}
 
    protected:
     virtual ~Observer() {}
   };
 
   typedef std::vector<DownloadItem*> DownloadVector;
 
   // Add all download items to |downloads|, no matter the type or state, without
   // clearing |downloads| first.
   virtual void GetAllDownloads(DownloadVector* downloads) = 0;
 
   // Called by a download source (Currently DownloadResourceHandler)
   // to initiate the non-source portions of a download.
   // Returns the id assigned to the download.  If the DownloadCreateInfo
   // specifies an id, that id will be used.
   virtual void StartDownload(
       scoped_ptr<DownloadCreateInfo> info,
       scoped_ptr<ByteStreamReader> stream,
       const DownloadUrlParameters::OnStartedCallback& on_started) = 0;
 
   // Remove downloads after remove_begin (inclusive) and before remove_end
-  // (exclusive). You may pass in null Time values to do an unbounded delete
+  // (exclusive). You may pass in null Time values to do an unbounded removal
   // in either direction.
   virtual int RemoveDownloadsBetween(base::Time remove_begin,
                                      base::Time remove_end) = 0;
 
-  // Remove downloads will delete all downloads that have a timestamp that is
-  // the same or more recent than |remove_begin|. The number of downloads
-  // deleted is returned back to the caller.
+  // Remove all downloads that have a timestamp that is the same or more recent
+  // than |remove_begin|. The number of downloads deleted is returned back to
+  // the caller.
   virtual int RemoveDownloads(base::Time remove_begin) = 0;
 
-  // Remove all downloads will delete all downloads. The number of downloads
-  // deleted is returned back to the caller.
+  // Remove all downloads. Returns the number of downloads removed.
   virtual int RemoveAllDownloads() = 0;
 
+  // Revives a removed download (undoes the removal).
+  virtual void ReviveDownload(uint32 id) = 0;
+
+  // Finalizes removal of a download. Downloads cannot be revived after this.
+  virtual void FinalizeRemoval(uint32 id) = 0;
+
   // See DownloadUrlParameters for details about controlling the download.
   virtual void DownloadUrl(scoped_ptr<DownloadUrlParameters> parameters) = 0;
 
   // Allow objects to observe the download creation process.
   virtual void AddObserver(Observer* observer) = 0;
 
   // Remove a download observer from ourself.
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Called by the embedder, after creating the download manager, to let it know
@@ skipping 36 matching lines @@
   virtual void CheckForHistoryFilesRemoval() = 0;
 
   // Get the download item for |id| if present, no matter what type of download
   // it is or state it's in.
   virtual DownloadItem* GetDownload(uint32 id) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_H_