Use a sound pool instead of a single audio tag.

ui/keyboard/resources/elements/kb-keyboard.html

 <!--
   -- Copyright 2013 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-element name="kb-keyboard" on-key-over="{{keyOver}}"
     on-key-up="{{keyUp}}" on-key-down="{{keyDown}}"
     on-key-longpress="{{keyLongpress}}" on-pointerup="{{up}}"
     on-pointerdown="{{down}}" on-pointerout="{{out}}"
@@ skipping 316 matching lines @@
 
       /**
        * Caches the specified sound on the keyboard.
        * @param {string} soundId The name of the .wav file in the "sounds"
            directory.
        */
       addSound: function(soundId) {
         // Check if already loaded.
         if (soundId == Sound.NONE || this.sounds[soundId])
           return;
-        var audio = document.createElement('audio');
-        audio.preload = "auto";
-        audio.id = soundId;
-        audio.src = "../sounds/" + soundId + ".wav";
-        audio.volume = this.volume;
-        this.sounds[soundId] = audio;
+        var pool = [];
+        for (var i = 0; i < SOUND_POOL_SIZE; i++) {
+          var audio = document.createElement('audio');
+          audio.preload = "auto";
+          audio.id = soundId;
+          audio.src = "../sounds/" + soundId + ".wav";
+          audio.volume = this.volume;
+          pool.push(audio);
+        }
+        this.sounds[soundId] = pool;
       },
 
       /**
        * Changes the current keyset.
        * @param {Object} detail The detail of the event that called this
        *     function.
        */
       changeKeyset: function(detail) {
         if (detail.relegateToShift && this.shift) {
           this.keyset = this.shift.textKeyset;
@@ skipping 181 matching lines @@
         if(this.changeKeyset(detail))
           return;
         if (detail.repeat) {
           this.keyTyped(detail);
           this.onNonControlKeyTyped();
           repeatKey.key = this.lastPressedKey;
           var self = this;
           repeatKey.timer = setTimeout(function() {
             repeatKey.timer = undefined;
             repeatKey.interval = setInterval(function() {
+               self.playSound(detail.sound);
                self.keyTyped(detail);
             }, REPEAT_INTERVAL_MSEC);
           }, Math.max(0, REPEAT_DELAY_MSEC - REPEAT_INTERVAL_MSEC));
         }
       },
 
       /**
        * Handles key-out event that is sent by kb-shift-key.
        * @param {CustomEvent} event The key-out event dispatched by
        *     kb-shift-key.
@@ skipping 237 matching lines @@
         }
       },
 
       /**
        * Plays the specified sound.
        * @param {Sound} sound The id of the audio tag.
        */
       playSound: function(sound) {
         if (!sound || sound == Sound.NONE)
           return;
-        var soundElement = this.sounds[sound];
-        if (!soundElement)
+        var pool = this.sounds[sound];
+        if (!pool) {
           console.error("Cannot find audio tag: " + sound);
-        else
-          soundElement.play();
+          return;
+        }
+        // Search the sound pool for a free resource.
+        for (var i = 0; i < pool.length; i++) {
+          if (pool[i].paused) {
+            pool[i].play();
+            return;
+          }
+        }
       },
 
       /**
        * Whether we should transit to upper case when seeing a space after
        * punctuation.
        * @return {boolean}
        */
       shouldUpperOnSpace: function() {
         // TODO(rsadam): Add other input types in which we should not
         // transition to upper after a space.
@@ skipping 88 matching lines @@
         if (this.alt)
           this.alt.onNonControlKeyTyped();
         this.classList.remove('ctrl-active');
         this.classList.remove('alt-active');
       },
 
       /**
        * Callback function for when volume is changed.
        */
       volumeChanged: function() {
-        var toChange = keys(this.sounds);
+        var toChange = Object.keys(this.sounds);
         for (var i = 0; i < toChange.length; i++) {
-          this.sounds[toChange[i]].volume = this.volume;
+          var pool = this.sounds[toChange[i]];
+          for (var j = 0; j < pool.length; j++) {
+            pool[j].volume = this.volume;
+          }
         }
       },
 
       /**
        * Id for the active keyset.
        * @type {string}
        */
       get activeKeysetId() {
         return this.layout + '-' + this.keyset;
       },
@@ skipping 110 matching lines @@
              }
           }
         }
         if (keysetsLoaded)
           console.error('No default keyset found for ' + this.layout);
         return false;
       }
     });
   </script>
 </polymer-element>