Fix issues that broke editing on browsers without Shadow DOM support.

dart/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 239 matching lines @@
   }
   if (tokenInfo == 'keyword') return currentTheme.keyword;
   if (tokenInfo == 'comment') return currentTheme.singleLineComment;
   if (tokenInfo == 'malformed input') {
     isMalformedInput = true;
     return new DiagnosticDecoration('error', tokenValue);
   }
   return currentTheme.foreground;
 }
 
-diagnostic(text, tip) {
-  if (text is String) {
-    text = new Text(text);
+diagnostic(content, tip) {
+  if (content is String) {
+    content = new Text(content);
+  }
+  if (content is! List) {
+    content = [content];
   }
   return new AnchorElement()
       ..classes.add('diagnostic')
-      ..append(text)
-      ..append(tip);
+      ..append(tip) // Should be first for better Firefox editing.
+      ..nodes.addAll(content);
 }