[Audio Player] Cleanup the code along with closure compiler

ui/file_manager/audio_player/elements/control_panel.js

Index: ui/file_manager/audio_player/elements/control_panel.js
diff --git a/ui/file_manager/audio_player/elements/control_panel.js b/ui/file_manager/audio_player/elements/control_panel.js
index 94c6db1d615cf9605dec15bc243e4da7669c4084..877f26eeafccb9c8047c25b641434d9ff1514f92 100644
--- a/ui/file_manager/audio_player/elements/control_panel.js
+++ b/ui/file_manager/audio_player/elements/control_panel.js
@@ -34,15 +34,26 @@
     return ~~(time / 60000) + ':' + ('0' + ~~(time / 1000 % 60)).slice(-2);
   }
 
-  Polymer('control-panel', {
+  /**
+   * @constructor
+   * @extends {PolymerElement}
+   */
+  var ControlPanelElement = function() {};
+
+  ControlPanelElement.prototype = {
     /**
      * Initializes an element. This method is called automatically when the
      * element is ready.
      */
     ready: function() {
       var onFocusoutBound = this.onVolumeControllerFocusout_.bind(this);
-      this.$.volumeSlider.addEventListener('focusout', onFocusoutBound);
-      this.$.volumeButton.addEventListener('focusout', onFocusoutBound);
+
+      this.volumeSlider = this.$.volumeSlider;
+      this.volumeButton = this.$.volumeButton;
+      this.volumeContainer = this.$.volumeContainer;
+
+      this.volumeSlider.addEventListener('focusout', onFocusoutBound);
+      this.volumeButton.addEventListener('focusout', onFocusoutBound);
     },
 
     /**
@@ -57,7 +68,7 @@
      * @param {AudioPlayerModel} newValue New Value.
      */
     modelChanged: function(oldValue, newValue) {
-      this.$.volumeSlider.model = newValue;
+      this.volumeSlider.model = newValue;
     },
 
     /**
@@ -136,7 +147,7 @@
 
     /**
      * Invoked the volume button is clicked.
-     * @type {Event} event The event.
+     * @param {!Event} event The event.
      */
     volumeButtonClick: function(event) {
       this.showVolumeController_(this.volumeSliderShown);
@@ -145,15 +156,15 @@
 
     /**
      * Invoked when the focus goes out of the volume elements.
-     * @param {FocusEvent} event The focusout event.
+     * @param {!FocusEvent} event The focusout event.
      * @private
      */
     onVolumeControllerFocusout_: function(event) {
       if (this.volumeSliderShown) {
         // If the focus goes out of the volume, hide the volume control.
         if (!event.relatedTarget ||
-            (event.relatedTarget !== this.$.volumeButton &&
-             event.relatedTarget !== this.$.volumeSlider)) {
+            (event.relatedTarget !== this.volumeButton &&
+             event.relatedTarget !== this.volumeSlider)) {
           this.showVolumeController_(false);
           this.volumeSliderShown = false;
         }
@@ -168,10 +179,12 @@
     showVolumeController_: function(show) {
       if (show) {
         matchBottomLine(this.$.volumeContainer, this.$.volumeButton);
-        this.$.volumeContainer.style.visibility = 'visible';
+        this.volumeContainer.style.visibility = 'visible';
       } else {
-        this.$.volumeContainer.style.visibility = 'hidden';
+        this.volumeContainer.style.visibility = 'hidden';
       }
     },
-  });
+  };
+
+  Polymer('control-panel', ControlPanelElement.prototype);
 })();  // Anonymous closure