Simplify volume manager in Files app.

chrome/browser/resources/file_manager/foreground/js/drive_banners.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';
 
 /**
  * Responsible for showing following banners in the file list.
  *  - WelcomeBanner
  *  - AuthFailBanner
@@ skipping 499 matching lines @@
       break;
     default:
       // If the current file system is neither the DOWNLOAD nor the DRIVE,
       // just hide the warning.
       this.showLowDownloadsSpaceWarning_(false);
       this.showLowDriveSpaceWarning_(false);
       return;
   }
 
   // If not mounted correctly, then do not continue.
-  if (!volume.root)
+  if (!volume.fileSystem)
     return;
 
   chrome.fileBrowserPrivate.getSizeStats(
-      volume.root.toURL(),
+      volume.fileSystem.root.toURL(),
       function(sizeStats) {
         var currentVolume = this.volumeManager_.getVolumeInfo(
             this.directoryModel_.getCurrentDirEntry());
         if (volume !== currentVolume) {
           // This happens when the current directory is moved during requesting
           // the file system size. Just ignore it.
           return;
         }
         // sizeStats is undefined, if some error occurs.
         if (!sizeStats || sizeStats.totalSize == 0)
@@ skipping 125 matching lines @@
  * @private
  */
 FileListBannerController.prototype.maybeShowAuthFailBanner_ = function() {
   var connection = this.volumeManager_.getDriveConnectionState();
   var showDriveNotReachedMessage =
       this.isOnCurrentProfileDrive() &&
       connection.type == util.DriveConnectionType.OFFLINE &&
       connection.reason == util.DriveConnectionReason.NOT_READY;
   this.authFailedBanner_.hidden = !showDriveNotReachedMessage;
 };