Disable sounds in the virtual keyboard.

ui/keyboard/resources/elements/kb-keyboard.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.
 
 /**
  * The repeat delay in milliseconds before a key starts repeating. Use the
  * same rate as Chromebook.
  * (See chrome/browser/chromeos/language_preferences.cc)
  * @const
  * @type {number}
@@ skipping 752 matching lines @@
       if (this.lastPressedKey)
         this.lastPressedKey.classList.remove('active');
     }
   },
 
   /**
    * Plays the specified sound.
    * @param {Sound} sound The id of the audio tag.
    */
   playSound: function(sound) {
-    if (!sound || sound == Sound.NONE)
+    if (!SOUND_ENABLED || !sound || sound == Sound.NONE)
       return;
     var pool = this.sounds[sound];
     if (!pool) {
       console.error("Cannot find audio tag: " + sound);
       return;
     }
     // Search the sound pool for a free resource.
     for (var i = 0; i < pool.length; i++) {
       if (pool[i].paused) {
         pool[i].play();
@@ skipping 183 matching lines @@
            keyboardLoaded();
            return true;
          }
       }
     }
     if (keysetsLoaded)
       console.error('No default keyset found for ' + this.layout);
     return false;
   }
 });