[Audio Player] Cleanup the code along with closure compiler

ui/file_manager/audio_player/elements/volume_controller.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('volume-controller', {
+  /**
+   * @constructor
+   * @extends {PolymerElement}
+   */
+  var VolumeControllerElement = function() {};
+
+  VolumeControllerElement.prototype = {
     /**
      * Initializes an element. This method is called automatically when the
      * element is ready.
      */
     ready: function() {
       this.style.width = this.width + 'px';
       this.style.height = this.height + 'px';
 
-      this.$.rawValueInput.style.width = this.height + 'px';
-      this.$.rawValueInput.style.height = this.width + 'px';
-      this.$.rawValueInput.style.webkitTransformOrigin =
+      this.rawValueInput = this.$.rawValueInput;
+      this.bar = this.$.bar;
+
+      this.rawValueInput.style.width = this.height + 'px';
+      this.rawValueInput.style.height = this.width + 'px';
+      this.rawValueInput.style.webkitTransformOrigin =
           (this.width / 2) + 'px ' +
           (this.width / 2 - 2) + 'px';
 
       var barLeft = (this.width / 2 - 1);
-      this.$.bar.style.left = barLeft + 'px';
-      this.$.bar.style.right = barLeft + 'px';
+      this.bar.style.left = barLeft + 'px';
+      this.bar.style.right = barLeft + 'px';
 
       this.addEventListener('keydown', this.onKeyDown_.bind(this));
     },
 
     /**
      * Registers handlers for changing of external variables
      */
     observe: {
       'model.volume': 'onVolumeChanged',
     },
@@ skipping 68 matching lines @@
         // Prevents the default behavior. These key should be handled in
         // <audio-player> element.
         case 'Up':
         case 'Down':
         case 'PageUp':
         case 'PageDown':
           event.preventDefault();
           break;
       }
     },
-  });
+  };
+
+  Polymer('volume-controller', VolumeControllerElement.prototype);
 })();  // Anonymous closure