Added custom tags helper classes to the Observatory

runtime/observatory/web/main.dart

Index: runtime/observatory/web/main.dart
diff --git a/runtime/observatory/web/main.dart b/runtime/observatory/web/main.dart
index 238bf97217a8bc40f0b7328393e4155747e8177b..41f3dc74c2c0f43a978edec47cc86685153cc87b 100644
--- a/runtime/observatory/web/main.dart
+++ b/runtime/observatory/web/main.dart
@@ -4,8 +4,9 @@
 
 import 'package:logging/logging.dart';
 import 'package:polymer/polymer.dart';
+import 'package:observatory/elements.dart';
 
-main() {
+main() async {
   Logger.root.level = Level.INFO;
   Logger.root.onRecord.listen((LogRecord rec) {
       if (rec.level == Level.WARNING &&
@@ -17,13 +18,10 @@ main() {
       }
       print('${rec.level.name}: ${rec.time}: ${rec.message}');
   });
+  await initElements();
   Logger.root.info('Starting Observatory');
-  initPolymer().then((zone) {
-    Logger.root.info('Polymer initialized');
-    // Code here is in the polymer Zone, which ensures that
-    // @observable properties work correctly.
-    Polymer.onReady.then((_) {
-      Logger.root.info('Polymer elements have been upgraded');
-    });
-  });
+  await initPolymer();
+  Logger.root.info('Polymer initialized');
+  await Polymer.onReady;
+  Logger.root.info('Polymer elements have been upgraded');
 }