Restore Mute button for Android media element.

Source/core/css/mediaControlsAndroid.css

 /*
  * Copyright (C) 2012 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 24 matching lines @@
 }
 
 video::-webkit-media-controls-enclosure {
     height: 40px;
 }
 
 audio::-webkit-media-controls-panel, video::-webkit-media-controls-panel {
     height: 35px;
 }
 
-audio::-webkit-media-controls-mute-button, video::-webkit-media-controls-mute-button {
-    display: none;
-}
-
 audio::-webkit-media-controls-play-button, video::-webkit-media-controls-play-button {
     width: 35px;
     height: 35px;
     line-height: 35px;
 }
 
 audio::-webkit-media-controls-current-time-display, video::-webkit-media-controls-current-time-display,
 audio::-webkit-media-controls-time-remaining-display, video::-webkit-media-controls-time-remaining-display {
     height: 35px;
     line-height: 35px;
@@ skipping 18 matching lines @@
     width: 35px;
     height: 35px;
     line-height: 35px;
 }
 
 video::-webkit-media-controls-toggle-closed-captions-button {
     width: 35px;
     height: 35px;
     line-height: 35px;
 }