Detect removed files and reflect the state in chrome://downloads and the download shelf

chrome/browser/download/download_shelf.cc

 // 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.
 
 #include "chrome/browser/download/download_shelf.h"
 
 #include "base/file_util.h"
 #include "chrome/browser/download/download_item.h"
 #include "chrome/browser/download/download_item_model.h"
 #include "chrome/browser/download/download_manager.h"
@@ skipping 52 matching lines @@
     default:
       NOTREACHED();
   }
   return string16();
 }
 
 bool DownloadShelfContextMenu::IsCommandIdEnabled(int command_id) const {
   switch (command_id) {
     case SHOW_IN_FOLDER:
     case OPEN_WHEN_COMPLETE:
-      return !download_->IsCancelled();
+      return !download_->IsCancelled() && download_->file_exists();
     case ALWAYS_OPEN_TYPE:
       return download_->CanOpenDownload();
     case CANCEL:
       return download_->IsPartialDownload();
     case TOGGLE_PAUSE:
       return download_->IsInProgress();
     default:
       return command_id > 0 && command_id < MENU_LAST;
   }
 }
@@ skipping 70 matching lines @@
       ALWAYS_OPEN_TYPE, IDS_DOWNLOAD_MENU_ALWAYS_OPEN_TYPE);
   finished_download_menu_model_->AddSeparator();
   finished_download_menu_model_->AddItemWithStringId(
       SHOW_IN_FOLDER, IDS_DOWNLOAD_MENU_SHOW);
   finished_download_menu_model_->AddSeparator();
   finished_download_menu_model_->AddItemWithStringId(
       CANCEL, IDS_DOWNLOAD_MENU_CANCEL);
 
   return finished_download_menu_model_.get();
 }