[Audio Player] Cleanup the code along with closure compiler

ui/file_manager/audio_player/elements/track_list.js

 // Copyright 2014 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.
 
 (function() {
   'use strict';
 
-  Polymer('track-list', {
+  /**
+   * @constructor
+   * @extends {PolymerElement}
+   */
+  var TrackListElement = function() {};
+
+  TrackListElement.prototype = {
     /**
      * Initializes an element. This method is called automatically when the
      * element is ready.
      */
     ready: function() {
       this.observeTrackList();
 
       window.addEventListener('resize', this.onWindowResize_.bind(this));
     },
 
@@ skipping 80 matching lines @@
 
       // Invalid index
       if (this.tracks.length === 0)
         this.currentTrackIndex = -1;
       else
         this.generatePlayOrder(false /* no need to keep the current track */);
     },
 
     /**
      * Invoked when 'tracks' property is changed.
-     * @param {Array.<TrackInfo>} oldValue Old value.
-     * @param {Array.<TrackInfo>} newValue New value.
+     * @param {Array.<AudioPlayer.TrackInfo>} oldValue Old value.
+     * @param {Array.<AudioPlayer.TrackInfo>} newValue New value.
      */
     tracksChanged: function(oldValue, newValue) {
       // Note: Sometimes both oldValue and newValue are null though the actual
       // values are not null. Maybe it's a bug of Polymer.
 
       // Re-register the observer of 'this.tracks'.
       this.observeTrackList();
 
       if (this.tracks.length !== 0) {
         // Restore the active track.
@@ skipping 132 matching lines @@
 
     /**
      * Request to replay the current music.
      */
     replayCurrentTrack: function() {
       this.fire('replay');
     },
 
     /**
      * Returns the current track.
-     * @param {AudioPlayer.TrackInfo} track TrackInfo of the current track.
+     * @return {AudioPlayer.TrackInfo} track TrackInfo of the current track.
      */
     getCurrentTrack: function() {
       if (this.tracks.length === 0)
         return null;
 
       return this.tracks[this.currentTrackIndex];
     },
 
     /**
      * Returns the next (or previous) track in the track list. If there is no
@@ skipping 23 matching lines @@
       if (newPlayOrder === -1 || newPlayOrder === this.tracks.length)
         return cyclic ? defaultTrackIndex : -1;
 
       var newTrackIndex = this.playOrder[newPlayOrder];
       console.assert(
           (0 <= newTrackIndex && newTrackIndex < this.tracks.length),
           'Insufficient TrackList.playOrder. New Play Order: ' + newPlayOrder);
 
       return newTrackIndex;
     },
-  });  // Polymer('track-list') block
+  };  // TrackListElement.prototype for 'track-list'
+
+  Polymer('track-list', TrackListElement.prototype);
 })();  // Anonymous closure