Divide volume_manager.js into files for each classes and extract interfaces from them.

ui/file_manager/file_manager/foreground/js/volume_manager_wrapper.js

 // Copyright 2013 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.
 
 /**
  * Thin wrapper for VolumeManager. This should be an interface proxy to talk
  * to VolumeManager. This class also filters Drive related data/events if
  * driveEnabled is set to false.
  *
  * @constructor
@@ skipping 30 matching lines @@
     queue.run(function(callNextStep) {
       chrome.runtime.getBackgroundPage(/** @type {function(Window=)} */(
           function(opt_backgroundPage) {
             this.backgroundPage_ = opt_backgroundPage;
             callNextStep();
           }.bind(this)));
     }.bind(this));
   }
 
   queue.run(function(callNextStep) {
-    this.backgroundPage_.VolumeManager.getInstance(function(volumeManager) {
-      this.onReady_(volumeManager);
-      callNextStep();
-    }.bind(this));
+    this.backgroundPage_.volumeManagerFactory.getInstance(
+        function(volumeManager) {
+          this.onReady_(volumeManager);
+          callNextStep();
+        }.bind(this));
   }.bind(this));
 }
 
 /**
  * Extends cr.EventTarget.
  */
 VolumeManagerWrapper.prototype.__proto__ = cr.EventTarget.prototype;
 
 /**
  * @param {VolumeManagerCommon.VolumeType} volumeType
@@ skipping 87 matching lines @@
  * @param {!Event} event Event object sent from VolumeManager.
  * @private
  */
 VolumeManagerWrapper.prototype.onEvent_ = function(event) {
   var eventVolumeType;
   switch (event.type) {
     case 'drive-connection-changed':
       eventVolumeType = VolumeManagerCommon.VolumeType.DRIVE;
       break;
     case 'externally-unmounted':
+      event = /** @type {!ExternallyUnmountedEvent} */ (event);
       eventVolumeType = event.volumeInfo.volumeType;
       break;
   }
 
-  if (this.isAllowedVolume_(eventVolumeType))
+  if (eventVolumeType && this.isAllowedVolume_(eventVolumeType))
     this.dispatchEvent(event);
 };
 
 /**
  * Called on events of modifying VolumeInfoList.
  * @param {Event} event Event object sent from VolumeInfoList.
  * @private
  */
 VolumeManagerWrapper.prototype.onVolumeInfoListUpdated_ = function(event) {
   if (this.allowedPaths_ === AllowedPaths.ANY_PATH) {
@@ skipping 193 matching lines @@
 };
 
 /**
  * Returns current state of VolumeManagerWrapper.
  * @return {string} Current state of VolumeManagerWrapper.
  */
 VolumeManagerWrapper.prototype.toString = function() {
   var initialized = this.isInitialized();
   var volumeManager = initialized ?
       this.volumeManager_ :
-      this.backgroundPage_.VolumeManager.getInstanceForDebug();
+      this.backgroundPage_.volumeManagerFactory.getInstanceForDebug();
 
   var str = 'VolumeManagerWrapper\n' +
       '- Initialized: ' + initialized + '\n';
 
   if (!initialized)
     str += '- PendingTasksCount: ' + this.pendingTasks_.length + '\n';
 
   return str + '- VolumeManager:\n' +
       '  ' + volumeManager.toString().replace(/\n/g, '\n  ');
 };