[mdv] implement Node.createBinding and Node.createBindings

pkg/mdv/lib/src/select_element.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 [SelectElement] API. */
 class _SelectElementExtension extends _ElementExtension {
-  _SelectedIndexBinding _valueBinding;
-
   _SelectElementExtension(SelectElement node) : super(node);
 
   SelectElement get node => super.node;
 
-  void bind(String name, model, String path) {
-    if (name.toLowerCase() == 'selectedindex') {
-      unbind('selectedindex');
-      node.attributes.remove('selectedindex');
-      _valueBinding = new _SelectedIndexBinding(node, model, path);
-      return;
+  NodeBinding createBinding(String name, model, String path) {
+    if (name.toLowerCase() === 'selectedindex') {
+      // TODO(rafaelw): Maybe template should remove all binding instructions.
+      node.attributes.remove(name);
+      return new _SelectedIndexBinding(node, model, path);
     }
-    super.bind(name, model, path);
-  }
-
-  void unbind(String name) {
-    if (name.toLowerCase() == 'selectedindex' && _valueBinding != null) {
-      _valueBinding.unbind();
-      _valueBinding = null;
-      return;
-    }
-    super.unbind(name);
-  }
-
-  void unbindAll() {
-    unbind('selectedindex');
-    super.unbindAll();
+    return super.createBinding(name, model, path);
   }
 }