Enable Try Dart to run on IE11.

site/try/src/editor.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.
 
 library trydart.editor;
 
 import 'dart:html';
 
 import 'package:compiler/implementation/scanner/scannerlib.dart' show
     EOF_TOKEN,
@@ skipping 143 matching lines @@
         hasSelection = node == anchorNode;
         anchorOffset = selection.anchorOffset;
         var alert;
         if (kind == 'error') {
           alert = error(message);
         } else if (kind == 'warning') {
           alert = warning(message);
         } else {
           alert = info(message);
         }
-        Element parent = node.parent;
+        Element parent = node.parentNode;
         if (parent.classes.contains("diagnostic") &&
             !interaction.oldDiagnostics.contains(parent)) {
           Element other = parent.firstChild;
           other.remove();
-          SpanElement wrapper = new SpanElement();
-          wrapper.style
-              ..fontWeight = 'normal';
+          SpanElement wrapper = new SpanElement()
+            ..classes.add('diagnostic')
+            ..style.fontWeight = 'normal';
+
           var root = getShadowRoot(wrapper);
           if (root is ShadowRoot) {
             // When https://code.google.com/p/chromium/issues/detail?id=313458
             // is fixed:
             // var link = new LinkElement()
             //     ..rel = "stylesheet"
             //     ..type = "text/css"
             //     ..href = "dartlang-style.css";
             // root.append(link);
             root.append(
@@ skipping 84 matching lines @@
     content = new Text(content);
   }
   if (content is! List) {
     content = [content];
   }
   return new AnchorElement()
       ..classes.add('diagnostic')
       ..append(tip) // Should be first for better Firefox editing.
       ..nodes.addAll(content);
 }