Dynamically load keyboard layouts.

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 461 matching lines @@
        * keyset for the new layout.
        */
       layoutChanged: function() {
         if (!this.selectDefaultKeyset()) {
           // Keyset selection fails if the keysets have not been loaded yet.
           var keysets = document.querySelector('#' + this.layout);
           if (keysets) {
             keyboard.appendChild(flattenKeysets(keysets.content));
             this.selectDefaultKeyset();
           } else {
-            console.error('Unable to find layout ' + this.layout);
+            // Add link for the keysets if missing from the document. Force
+            // a layout change after resolving the import of the link.
+            var query = 'link[id=' + this.layout + ']';
+            if (!document.querySelector(query)) {
+              // Layout has not beeen loaded yet.
+              var link = document.createElement('link');
+              link.id = this.layout;
+              link.setAttribute('rel', 'import');
+              link.setAttribute('href', 'layouts/' + this.layout + '.html');
+              document.head.appendChild(link);
+
+              // Load content for the new link element.
+              var self = this;
+              HTMLImports.importer.load(document, function() {
+                HTMLImports.parser.parseLink(link);

[bshe, 2013/09/06 21:12:21]

would it enter infinite loop if failed to load?

[kevers, 2013/09/09 15:44:04]

We do a check for an existing link element before injecting a new link.  If the
load fails, the next call to layoutChanged will detect that a link element was
already added and not do any extra recursion.

+                self.layoutChanged();
+              });
+            }
           }
         }
         this.classList.remove('caps-locked');
         this.cacheCapsLock();
       },
 
       /**
        * Caches the keyset transitions required when caps lock is enabled.
        */
       cacheCapsLock: function() {
@@ skipping 37 matching lines @@
           }
         }
         if (keysetsLoaded)
           console.error('No default keyset found for ' + this.layout);
         return false;
       }
     });
   </script>
 </polymer-element>