Removed polymer & mirror from Observatory

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

+// 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';
+
+navMenu(String label, {String link: '', Iterable<Element> content: const []}) {
+  assert(label != null);
+  assert(content != null);
+  assert(link != null);
+  return new LIElement()..classes = ['nav-menu']
+    ..children = [
+      new SpanElement()..classes = ['nav-menu_label']
+        ..children = [
+          new AnchorElement(href: link)
+            ..text = label,
+          new UListElement()
+            ..children = content
+        ]
+    ];
+}