AudioPlayer: Update layout to show the volume slider without using popup.

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({
   is: 'audio-player',
 
   properties: {
     /**
      * Flag whether the audio is playing or paused. True if playing, or false
@@ skipping 421 matching lines @@
       }
     }
   },
 
   /**
    * Invoked when the 'keydown' event is fired.
    * @param {Event} event The event object.
    */
   onKeyDown_: function(event) {
     switch (event.keyIdentifier) {
-      case 'Up':
-        if (this.$.audioController.volumeSliderShown && this.model.volume < 100)
-          this.model.volume += 1;
-        break;
-      case 'Down':
-        if (this.$.audioController.volumeSliderShown && this.model.volume > 0)
-          this.model.volume -= 1;
-        break;
-      case 'PageUp':
-        if (this.$.audioController.volumeSliderShown && this.model.volume < 91)
-          this.model.volume += 10;
-        break;
-      case 'PageDown':
-        if (this.$.audioController.volumeSliderShown && this.model.volume > 9)
-          this.model.volume -= 10;
-        break;
       case 'MediaNextTrack':
         this.onControllerNextClicked();
         break;
       case 'MediaPlayPause':
         this.playing = !this.playing;
         break;
       case 'MediaPreviousTrack':
         this.onControllerPreviousClicked();
         break;
       case 'MediaStop':
         // TODO: Define "Stop" behavior.
         break;
     }
   },
 
   /**
    * Computes volume value for audio element. (should be in [0.0, 1.0])
    * @param {number} volume Volume which is set in the UI. ([0, 100])
    * @return {number}
    */
   computeAudioVolume_: function(volume) {
     return volume / 100;
   }
 });