Build Observatory as part of runtime

runtime/observatory/test/inbound_references_test.dart

 // Copyright (c) 2014, 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 inbound_references_test;
 
 import 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
@@ skipping 37 matching lines @@
           hasReferenceSuchThat((r) => r['slot'] == 1 &&
                                       r['source'].isList);
           hasReferenceSuchThat((r) => r['slot']=='<unknown>' &&
                                       r['source'] is Field);
     });
 }),
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);