Build Observatory as part of runtime

runtime/observatory/test/allocations_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 allocations_test;
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
@@ skipping 14 matching lines @@
     return lib.classes.first.load().then((Class fooClass) {
       expect(fooClass.name, equals('Foo'));
       expect(fooClass.newSpace.accumulated.instances +
              fooClass.oldSpace.accumulated.instances, equals(3));
     });
 }),
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);