Obtain downloads dir entry from VolumeManager.

chrome/browser/resources/file_manager/js/file_tasks.js

 // 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.
 
 'use strict';
 
 /**
  * This object encapsulates everything related to tasks execution.
  *
  * @param {FileManager} fileManager FileManager instance.
@@ skipping 538 matching lines @@
   };
 
   galleryFrame.onload = function() {
     galleryFrame.contentWindow.ImageUtil.metrics = metrics;
 
     // TODO(haruki): isOnReadonlyDirectory() only checks the permission for the
     // root. We should check more granular permission to know whether the file
     // is writable or not.
     var readonly = fm.isOnReadonlyDirectory();
     var currentDir = fm.directoryModel_.getCurrentDirEntry();
-    var downloadsDir = fm.directoryModel_.getRootsList().item(0);
+    var downloadsVolume =
+        fm.volumeManager_.getVolumeInfo(RootDirectory.DOWNLOADS);
+    var downloadsDir = downloadsVolume && downloadsVolume.root;
     var readonlyDirName = null;
     if (readonly) {
       readonlyDirName = fm.isOnDrive() ?
           PathUtil.getRootLabel(PathUtil.getRootPath(currentDir.fullPath)) :
           fm.directoryModel_.getCurrentRootName();
     }
 
     var context = {
       // We show the root label in readonly warning (e.g. archive name).
       readonlyDirName: readonlyDirName,
@@ skipping 150 matching lines @@
       items, defaultIdx,
       function(item) {
         onSuccess(item.task);
       });
 };
 
 FileTasks.decorate('display');
 FileTasks.decorate('updateMenuItem');
 FileTasks.decorate('execute');
 FileTasks.decorate('executeDefault');