Wrapping leaf nodes in non polymer elements

runtime/observatory/lib/src/elements/helpers/tag.dart

Index: runtime/observatory/lib/src/elements/helpers/tag.dart
diff --git a/runtime/observatory/lib/src/elements/helpers/tag.dart b/runtime/observatory/lib/src/elements/helpers/tag.dart
new file mode 100644
index 0000000000000000000000000000000000000000..386dedd197a7330d89e30938e0c1794e965a3858
--- /dev/null
+++ b/runtime/observatory/lib/src/elements/helpers/tag.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2016, 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.
+
+import 'dart:html';
+
+class Tag<T> {
+  final String name;
+
+  const Tag(this.name);
+
+  static final Map<Type, String> _tagByClass = <Type, String>{};
+  static final Map<String, Type> _classByTag = <String, Type>{};
+
+  void ensureRegistration() {
+    if (!_tagByClass.containsKey(T) && !_classByTag.containsKey(name)) {
+      document.registerElement(name, T);
+      _tagByClass[T] = name;
+      _classByTag[name] = T;
+    }
+    if (_tagByClass[T] != name)
+      throw new ArgumentError(
+        'Class $T is already registered to tag ${_tagByClass[T]}');
+    if (_classByTag[name] != T)
+      throw new ArgumentError(
+        'Tag $name is already registered by class ${_classByTag[name]}');
+  }
+}