work around for https://github.com/Polymer/TemplateBinding/issues/150

pkg/template_binding/lib/src/template.dart

Index: pkg/template_binding/lib/src/template.dart
diff --git a/pkg/template_binding/lib/src/template.dart b/pkg/template_binding/lib/src/template.dart
index 552c5cf3baa3fae3ae60d469bc327c7f15b6bdb4..8df84d1bbd28ec5ac621f7a39d59d9fc1ed47957 100644
--- a/pkg/template_binding/lib/src/template.dart
+++ b/pkg/template_binding/lib/src/template.dart
@@ -116,7 +116,7 @@ class TemplateBindExtension extends _ElementExtension {
     if (map == null) {
       // TODO(rafaelw): Setup a MutationObserver on content to detect
       // when the instanceMap is invalid.
-      map = new _InstanceBindingMap(content, delegate);
+      map = _createInstanceBindingMap(content, delegate);
       ref._bindingMap = map;
     }