port TemplateBinding to ed3266266e751b5ab1f75f8e0509d0d5f0ef35d8

pkg/template_binding/lib/src/element.dart

Index: pkg/template_binding/lib/src/element.dart
diff --git a/pkg/template_binding/lib/src/element.dart b/pkg/template_binding/lib/src/element.dart
index c3c4992f39cb95d2dfcb4c06b1faf9db1cb46762..1ee43f9317cab70eefa81464d32ba762bc29a58b 100644
--- a/pkg/template_binding/lib/src/element.dart
+++ b/pkg/template_binding/lib/src/element.dart
@@ -15,7 +15,7 @@ class _ElementExtension extends NodeBindExtension {
     if (_node is OptionElement && name == 'value') {
       // Note: because <option> can be a semantic template, <option> will be
       // a TemplateBindExtension sometimes. So we need to handle it here.
-      _node.attributes.remove(name);
+      (_node as OptionElement).attributes.remove(name);
       binding = new _OptionValueBinding(_node, model, path);
     } else {
       binding = new _AttributeBinding(_node, name, model, path);