Implement support for single stepping out of an async function.

runtime/observatory/tests/service/step_over_await_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  --verbose_debug
 
 import 'dart:async';
 import 'dart:developer';
 
 import 'test_helper.dart';
 import 'service_test_common.dart';
 
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 const int LINE_A = 22;
 const int LINE_B = 24;
 
-// This tests the asyncStepOver command.
+// This tests the asyncNext command.
 asyncFunction() async {
   debugger();
   print('a'); // LINE_A
   await new Future.delayed(new Duration(seconds: 2));
   print('b'); // LINE_B
 }
 
 testMain() {
   asyncFunction();
 }
 
 var tests = [
   hasStoppedAtBreakpoint,
   stoppedAtLine(LINE_A),
   stepOver, // At new Duration().
   stepOver, // At new Future.delayed().
   stepOver, // At async.
   // Check that we are at the async statement
   (Isolate isolate) async {
     expect(M.isAtAsyncSuspension(isolate.pauseEvent), isTrue);
   },
-  asyncStepOver,
+  asyncNext,
+  hasStoppedAtBreakpoint,
   stoppedAtLine(LINE_B),
   resumeIsolate,
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testMain);