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

chrome/app/chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- ChromeOS-specific strings (included from generated_resources.grd).
      Everything in this file is wrapped in <if expr="chromeos">. -->
 <grit-part>
   <message name="IDS_EMPTY_STRING" desc="Empty string, exist only to make code generic. No translation required.">
   </message>
   <!-- Idle logout dialog for retail mode -->
   <message name="IDS_IDLE_LOGOUT_TITLE" desc="Dialog title for the idle logout dialog. Used in retail mode only.">
     Are you still there?
   </message>
@@ skipping 1038 matching lines @@
     Volume slider
   </message>
 
 <!-- Audio Player -->
   <message name="IDS_AUDIO_PLAYER_SHUFFLE_BUTTON_LABEL" desc="Label for the Shuffle button of audio player.">
     Shuffle
   </message>
   <message name="IDS_AUDIO_PLAYER_REPEAT_BUTTON_LABEL" desc="Label for the Repeat button of audio player">
     Repeat
   </message>
-  <message name="IDS_AUDIO_PLAYER_OPEN_VOLUME_SLIDER_BUTTON_LABEL" desc="Label for a button which is used to open volume slider in audio player.">
-    Open volume slider
-  </message>
   <message name="IDS_AUDIO_PLAYER_OPEN_PLAY_LIST_BUTTON_LABEL" desc="Label for a button which is used to open play list in audio player.">
     Open play list
   </message>
 
 <!-- Video Player -->
   <message name="IDS_VIDEO_PLAYER_PLAY_THIS_COMPUTER" desc="In the video player app, message of menu item which is shown at the top of the list of Chromecasts. This menuitem is to play the video on this computer (locally), intead of on TVs with Chromecast.">
     This computer
   </message>
   <message name="IDS_VIDEO_PLAYER_PLAYING_ON" desc="In the video player app, message is shown ahead of the name of the current chromecast which plays the video now. For example, if this message is 'Playing on' and the Chromecast name is 'Foocast', 'Playing on Foocast' is shown.">
     Playing on
@@ skipping 5316 matching lines @@
     Installing
   </message>
   <message name="IDS_FLAGS_PRINTER_PROVIDER_SEARCH_APP_NAME" desc="Name of the flag used to enable launching Chrome Web Store Gallery widget app for searching for printer provider apps.">
     Chrome Web Store Gallery app for printer drivers
   </message>
   <message name="IDS_FLAGS_PRINTER_PROVIDER_SEARCH_APP_DESCRIPTION" desc="Description of a flag in chrome://flags that enables launching Chrome Web Store Gallery widget app for searching for printer provider apps.">
     Enables Chrome Web Store Gallery app for printer drivers. The app searches Chrome Web Store for extensions that support printing to a USB printer with specific USB ID.
   </message>
 
 </grit-part>