No need to pass DownloadItemModel ownership.

chrome/browser/download/download_shelf_context_menu.h

 // Copyright (c) 2011 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_DOWNLOAD_SHELF_CONTEXT_MENU_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SHELF_CONTEXT_MENU_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/string16.h"
+#include "content/public/browser/download_item.h"
 #include "ui/base/models/simple_menu_model.h"
 
-class DownloadItemModel;
-
 namespace content {
-class DownloadItem;
 class PageNavigator;
 }
 
 // This class is responsible for the download shelf context menu. Platform
 // specific subclasses are responsible for creating and running the menu.
-class DownloadShelfContextMenu : public ui::SimpleMenuModel::Delegate {
+//
+// The DownloadItem corresponding to the context menu is observed for removal or
+// destruction.
+class DownloadShelfContextMenu : public ui::SimpleMenuModel::Delegate,
+                                 public content::DownloadItem::Observer {
  public:
   enum ContextMenuCommands {
     SHOW_IN_FOLDER = 1,    // Open a folder view window with the item selected.
     OPEN_WHEN_COMPLETE,    // Open the download when it's finished.
     ALWAYS_OPEN_TYPE,      // Default this file extension to always open.
     CANCEL,                // Cancel the download.
     TOGGLE_PAUSE,          // Temporarily pause a download.
     DISCARD,               // Discard the malicious download.
     KEEP,                  // Keep the malicious download.
     LEARN_MORE_SCANNING,   // Show information about download scanning.
     LEARN_MORE_INTERRUPTED,// Show information about interrupted downloads.
   };
 
   virtual ~DownloadShelfContextMenu();
 
   content::DownloadItem* download_item() const { return download_item_; }
-  void set_download_item(content::DownloadItem* item) { download_item_ = item; }
 
  protected:
-  DownloadShelfContextMenu(DownloadItemModel* download_model,
+  DownloadShelfContextMenu(content::DownloadItem* download_item,
                            content::PageNavigator* navigator);
 
-  // Returns the correct menu model depending whether the download item is
-  // completed or not.
+  // Returns the correct menu model depending on the state of the download item.
+  // Returns NULL if the download was destroyed.
   ui::SimpleMenuModel* GetMenuModel();
 
   // ui::SimpleMenuModel::Delegate:
   virtual bool IsCommandIdEnabled(int command_id) const OVERRIDE;
   virtual bool IsCommandIdChecked(int command_id) const OVERRIDE;
   virtual void ExecuteCommand(int command_id) OVERRIDE;
   virtual bool GetAcceleratorForCommandId(
       int command_id,
       ui::Accelerator* accelerator) OVERRIDE;
   virtual bool IsItemForCommandIdDynamic(int command_id) const OVERRIDE;
   virtual string16 GetLabelForCommandId(int command_id) const OVERRIDE;
 
  private:
+  // Detaches self from |download_item_|. Called when the DownloadItem is
+  // destroyed or when this object is being destroyed.
+  void DetachFromDownloadItem();
+
+  // content::DownloadItem::Observer
+  virtual void OnDownloadDestroyed(content::DownloadItem* download) OVERRIDE;
+
   ui::SimpleMenuModel* GetInProgressMenuModel();
   ui::SimpleMenuModel* GetFinishedMenuModel();
   ui::SimpleMenuModel* GetInterruptedMenuModel();
   ui::SimpleMenuModel* GetMaliciousMenuModel();
 
   // We show slightly different menus if the download is in progress vs. if the
   // download has finished.
   scoped_ptr<ui::SimpleMenuModel> in_progress_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> finished_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> interrupted_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> malicious_download_menu_model_;
 
-  // A model to control the cancel behavior.
-  DownloadItemModel* download_model_;
-
   // Information source.
   content::DownloadItem* download_item_;
 
   // Used to open tabs.
   content::PageNavigator* navigator_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadShelfContextMenu);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SHELF_CONTEXT_MENU_H_