Implement rewind: drop one or more frames from the debugger.

runtime/observatory/tests/service/set_vm_name_rpc_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 --vm-name=Walter
 
 import 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
@@ skipping 14 matching lines @@
     });
     
     var result = await vm.setName('Barbara');
     expect(result.type, equals('Success'));
 
     await completer.future;
     expect(vm.name, equals('Barbara'));
   },
 ];
 
-main(args) async => runVMTests(args, tests, trace_service: true);
+main(args) async => runVMTests(args, tests,
+                               extraArgs: [ '--trace-service',
+                                            '--trace-service-verbose' ]);