fix packages for latest SDK changes

pkg/mdv/lib/src/node.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of mdv;
 
 /** Extensions to the [Node] API. */
 class _NodeExtension {
   final Node node;
   Map<String, NodeBinding> _bindings;
 
   _NodeExtension(this.node);
 
   NodeBinding createBinding(String name, model, String path) => null;
 
   /**
    * Binds the attribute [name] to the [path] of the [model].
    * Path is a String of accessors such as `foo.bar.baz`.
    */
   NodeBinding bind(String name, model, String path) {
     var binding = bindings[name];
-    if (binding != null)  binding.close();
+    if (binding != null) binding.close();
 
-    binding = createBinding(name, model, path);
+    // Note: dispatch through the xtag so a custom element can override it.
+    binding = (node is Element ? (node as Element).xtag : node)
+        .createBinding(name, model, path);
+
     bindings[name] = binding;
     if (binding == null) {
       window.console.error('Unhandled binding to Node: '
           '$this $name $model $path');
     }
     return binding;
   }
 
   /** Unbinds the attribute [name]. */
   void unbind(String name) {
@@ skipping 85 matching lines @@
   void close() {
     if (closed) return;
 
     if (_pathSub != null) _pathSub.cancel();
     _pathSub = null;
     _observer = null;
     _node = null;
     _model = null;
   }
 }