downloads: add the ability to undo download removal.

content/public/browser/download_item.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.
 //
 // Each download is represented by a DownloadItem, and all DownloadItems
 // are owned by the DownloadManager which maintains a global list of all
 // downloads. DownloadItems are created when a user initiates a download,
 // and exist for the duration of the browser life time.
 //
 // Download observers:
@@ skipping 45 matching lines @@
 
     // Download is completely finished.
     COMPLETE,
 
     // Download has been cancelled.
     CANCELLED,
 
     // This state indicates that the download has been interrupted.
     INTERRUPTED,
 
+    // The user removed this download from their history.

[benjhayden, 2014/11/13 18:01:59]

Clarify that the state is not terminal?
"The user removed this download from history but may undo the removal."?

+    REMOVED,
+
     // Maximum value.
     MAX_DOWNLOAD_STATE
   };
 
   // How the final target path should be used.
   enum TargetDisposition {
     TARGET_DISPOSITION_OVERWRITE, // Overwrite if the target already exists.
     TARGET_DISPOSITION_PROMPT     // Prompt the user for the actual
                                   // target. Implies
                                   // TARGET_DISPOSITION_OVERWRITE.
@@ skipping 55 matching lines @@
   // exit (DownloadManager destructor) from user interface initiated cancels
   // because at exit, the history system may not exist, and any updates to it
   // require AddRef'ing the DownloadManager in the destructor which results in
   // a DCHECK failure. Set |user_cancel| to false when canceling from at
   // exit to prevent this crash. This may result in a difference between the
   // downloaded file's size on disk, and what the history system's last record
   // of it is. At worst, we'll end up re-downloading a small portion of the file
   // when resuming a download (assuming the server supports byte ranges).
   virtual void Cancel(bool user_cancel) = 0;
 
+  // Marks the download as removed but doesn't actually delete it yet. This
+  // behavior is used from chrome://downloads so removal can be undone.
+  virtual void MarkRemoved() = 0;
+
+  // Undoes the effects of MarkRemoved() and restores the download's |status_|

[benjhayden, 2014/11/13 18:01:59]

This is an interface, so let's say something like "restores the value of
GetState() to its prior value" to avoid implementation details?

+  // to |prev_status_|. Used from chrome://downloads so removal can be undone.
+  virtual void UndoRemove() = 0;
+
   // Removes the download from the views and history. If the download was
   // in-progress or interrupted, then the intermediate file will also be
   // deleted.
   virtual void Remove() = 0;
 
   // Open the file associated with this download.  If the download is
   // still in progress, marks the download to be opened when it is complete.
   virtual void OpenDownload() = 0;
 
   // Show the download via the OS shell.
@@ skipping 178 matching lines @@
   // return |name|. Has no effect on the final target filename.
   virtual void SetDisplayName(const base::FilePath& name) = 0;
 
   // Debug/testing -------------------------------------------------------------
   virtual std::string DebugString(bool verbose) const = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_ITEM_H_