[Audio Player] Cleanup the code along with closure compiler

ui/file_manager/audio_player/elements/audio_player.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.
 
-Polymer('audio-player', {
-  /**
-   * Child Elements
-   */
+/**
+ * @constructor
+ * @extends {PolymerElement}
+ */
+var AudioPlayerElement = function() {};
+
+AudioPlayerElement.prototype = {
+  // Child Elements
   audioController: null,
   audioElement: null,
   trackList: null,
 
+  // Published values
+  playing: true,
+  currenttrackurl: '',
+  playcount: 0,
+
   // Attributes of the element (lower characters only).
   // These values must be used only to data binding and shouldn't be assigned
   // any value nowhere except in the handler.
   publish: {
     playing: {
       value: true,
       reflect: true
     },
     currenttrackurl: {
       value: '',
@@ skipping 214 matching lines @@
         this.trackList.currentTrackIndex == nextTrackIndex) {
       this.audioElement.play();
     }
 
     this.trackList.currentTrackIndex = nextTrackIndex;
   },
 
   /**
    * Timeout ID of auto advance. Used internally in scheduleAutoAdvance_() and
    *     cancelAutoAdvance_().
-   * @type {number}
+   * @type {number?}
    * @private
    */
   autoAdvanceTimer_: null,
 
   /**
    * Schedules automatic advance to the next track after a timeout.
    * @param {boolean} forward True if next, false if previous.
    * @param {boolean} repeat True if repeat-mode is enabled. False otherwise.
    * @private
    */
@@ skipping 110 matching lines @@
         this.onControllerPlayingChanged(playing, !playing);
         break;
       case 'MediaPreviousTrack':
         this.onControllerPreviousClicked();
         break;
       case 'MediaStop':
         // TODO: Define "Stop" behavior.
         break;
     }
   },
-});
+};
+
+Polymer('audio-player', AudioPlayerElement.prototype);