Refactor service tests in preparation of running on sky_shell

runtime/observatory/tests/service/reachable_size_test.dart

 // Copyright (c) 2015, 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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
+import 'service_test_common.dart';
 
 class Pair {
   var x, y;
 }
 
 var p1;
 var p2;
 
 buildGraph() {
   p1 = new Pair();
@@ skipping 43 matching lines @@
   expect(p2_shallow, lessThan(p2_retained));
   expect(p2_retained, lessThan(p2_reachable));
 
   expect(p1_shallow, equals(p2_shallow));
   expect(p1_retained, equals(p2_retained));
   expect(p1_reachable, equals(p2_reachable));
 },
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: buildGraph);