Implement virtual keyboard hiding.

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-enable-sel="enableSel"
     on-enable-dbl="enableDbl" attributes="keyset layout rows capsLocked">
@@ skipping 391 matching lines @@
         var toKeysetId = detail.toKeyset;
         // Keyset transition key.
         if (toKeysetId) {
           this.keyset = toKeysetId;
           this.querySelector('#' + this.layout + '-' + this.keyset).nextKeyset =
               detail.nextKeyset;
         }
         var toLayoutId = detail.toLayout;
         // Layout transition key.
         if (toLayoutId)
-          this.layout = toLayoutId;
+          hideKeyboard();
         var char = detail.char;
         if (enterUpperOnSpace) {
           enterUpperOnSpace = false;
           if (char == ' ')
             this.keyset = 'upper';
         }
         switch(char) {
           case 'Invalid':
             swipeStatus.swipeFlags = 0;
             return;
@@ skipping 107 matching lines @@
           }
         }
         if (keysetsLoaded)
           console.error('No default keyset found for ' + this.layout);
         return false;
       }
     });
   </script>
 </polymer-element>