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

runtime/observatory/tests/service/step_over_await_test.dart

Index: runtime/observatory/tests/service/step_over_await_test.dart
diff --git a/runtime/observatory/tests/service/step_over_await_test.dart b/runtime/observatory/tests/service/step_over_await_test.dart
index 1bbb3b791b7729ee340eca141fd378a6f0dc418c..d5f946cb937cc51fc4b6030c71b17d6d5397f833 100644
--- a/runtime/observatory/tests/service/step_over_await_test.dart
+++ b/runtime/observatory/tests/service/step_over_await_test.dart
@@ -1,7 +1,7 @@
 // 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  --verbose_debug --trace_service
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
 
 import 'dart:async';
 import 'dart:developer';