Use a sound pool instead of a single audio tag.

ui/keyboard/resources/elements/kb-key-base.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-key-base"
     on-pointerout="{{out}}"
     attributes="char invert repeat hintText toKeyset toLayout">
   <script>
@@ skipping 163 matching lines @@
        */
       get hintTextValue() {
         return this.invert ? (this.char || this.textContent) : this.hintText;
       },
 
       /**
        * Handles a swipe flick that originated from this key.
        * @param {detail} The details of the swipe.
        */
       onFlick: function(detail) {
-        if (!(detail.direction & SWIPE_DIRECTION.UP) || !this.hintTextValue)
+        if (!(detail.direction & SwipeDirection.UP) || !this.hintTextValue)
           return;
         var typeDetails = {char: this.hintTextValue};
         this.fire('type-key', typeDetails);
       },
 
       /**
        * Returns a subset of the key attributes.
        * @param {string} caller The id of the function which called
        *     populateDetails.
        */
@@ skipping 32 matching lines @@
           if (this.keysetRules && this.keysetRules.long != undefined) {
             detail.toKeyset = this.keysetRules.long[TO_KEYSET - OFFSET];
             detail.nextKeyset = this.keysetRules.long[NEXT_KEYSET - OFFSET];
           }
           this.fire('key-longpress', detail);
         }, null, LONGPRESS_DELAY_MSEC);
       },
     });
   </script>
 </polymer-element>