Build Observatory as part of runtime

runtime/observatory/lib/src/elements/observatory_application.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 observatory_application_element;
 
 import 'observatory_element.dart';
 import 'package:observatory/app.dart';
 import 'package:polymer/polymer.dart';
 
@@ skipping 10 matching lines @@
   @override
   void attached() {
     super.attached();
     if (devtools) {
       app = new ObservatoryApplication.devtools(this);
     } else {
       app = new ObservatoryApplication(this);
     }
   }
 }