Add layout switcher for virtual keyboard.

ui/keyboard/resources/elements/kb-keyset.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-keyset" attributes="nextKeyset isDefault
-    capsLocksTo capsLockable" on-key-up="keyUp"
-    on-key-longpress="keyLongpress">
+    capsLocksTo capsLockable" on-key-up="keyUp" on-key-longpress="keyLongpress">
   <template>
     <style>
       @host {
         * {
           -webkit-box-orient: vertical;
           -webkit-box-flex: 1;
           display: -webkit-box;
         }
       }
     </style>
@@ skipping 49 matching lines @@
         var leftOffset = activeAltKeySet.offset * event.target.clientWidth;
         activeAltKeySet.style.left = event.target.offsetLeft - leftOffset +
             'px';
         var nodes = activeAltKeySet.childNodes;
         nodes[activeAltKeySet.offset].classList.add('active');
         altkeyContainer.hidden = false;
       }
     });
   </script>
 </polymer-element>