fix packages for latest SDK changes

pkg/mdv/lib/src/node.dart

Index: pkg/mdv/lib/src/node.dart
diff --git a/pkg/mdv/lib/src/node.dart b/pkg/mdv/lib/src/node.dart
index d2fa6d40c7b239734dfae4d7c33a9ed5a73f3fc1..d5eb1121800518ee2102b595dc1051d6a7bf9f6f 100644
--- a/pkg/mdv/lib/src/node.dart
+++ b/pkg/mdv/lib/src/node.dart
@@ -19,9 +19,12 @@ class _NodeExtension {
    */
   NodeBinding bind(String name, model, String path) {
     var binding = bindings[name];
-    if (binding != null)  binding.close();
+    if (binding != null) binding.close();
+
+    // Note: dispatch through the xtag so a custom element can override it.
+    binding = (node is Element ? node.xtag : node)
+        .createBinding(name, model, path);
 
-    binding = createBinding(name, model, path);
     bindings[name] = binding;
     if (binding == null) {
       window.console.error('Unhandled binding to Node: '