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

pkg/template_binding/lib/src/template.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 template_binding;
 
 /** Extensions to [Element]s that behave as templates. */
 class TemplateBindExtension extends _ElementExtension {
   var _model;
   BindingDelegate _bindingDelegate;
@@ skipping 98 matching lines @@
   DocumentFragment createInstance([model, BindingDelegate delegate,
       List<NodeBinding> bound]) {
     var ref = templateBind(this.ref);
     var content = ref.content;
     // Dart note: we store _bindingMap on the TemplateBindExtension instead of
     // the "content" because we already have an expando for it.
     var map = ref._bindingMap;
     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;
     }
 
     var staging = _getTemplateStagingDocument();
     var instance = _deepCloneIgnoreTemplateContent(content, staging);
 
     _addMapBindings(instance, map, model, delegate, bound);
     // TODO(rafaelw): We can do this more lazily, but setting a sentinel
     // in the parent of the template element, and creating it when it's
     // asked for by walking back to find the iterating template.
@@ skipping 310 matching lines @@
     node = node.parentNode;
   }
 
   // Note: JS code tests that getElementById is present. We can't do that
   // easily, so instead check for the types known to implement it.
   if (node is Document || node is ShadowRoot || node is SvgSvgElement) {
     return node;
   }
   return null;
 }