update MDV impl

pkg/mdv/lib/src/bindings.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;
 
 // This code is a port of Model-Driven-Views:
 // https://github.com/polymer-project/mdv
 // The code mostly comes from src/template_element.js
 
@@ skipping 411 matching lines @@
   }
 
   getInstanceFragment(syntax) {
     if (syntax != null) {
       return syntax.getInstanceFragment(_templateElement);
     }
     return _templateElement.createInstance();
   }
 
   void _handleChanges(List<ChangeRecord> splices) {
-    var syntax = TemplateElement.syntax[_templateElement.attributes['syntax']];
+    var template = _templateElement;
+    var syntax = TemplateElement.syntax[template.attributes['syntax']];
+
+    if (template.parentNode == null || template.document.window == null) {
+      // TODO(jmesserly): this is a little different than the MDV code, which
+      // removes _templateIterator from all instances (via the weak table).
+      // I think it has a similar effect. It might be a no-op.
+      removeAllInstances();
+      abandon();
+      return;
+    }
 
     for (var splice in splices) {
       if (splice is! ListChangeRecord) continue;
 
       for (int i = 0; i < splice.removedCount; i++) {
         removeInstanceAt(splice.index);
       }
 
       for (var addIndex = splice.index;
           addIndex < splice.index + splice.addedCount;
@@ skipping 13 matching lines @@
 
   void unobserve() {
     if (_sub == null) return;
     _sub.cancel();
     _sub = null;
   }
 
   void abandon() {
     unobserve();
     _valueBinding.cancel();
+    terminators.clear();
     inputs.dispose();
   }
 }