Async-step, first cut.

runtime/observatory/tests/service/async_step_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=--compile_all --error_on_bad_type --error_on_bad_override  --verbose_debug
+
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+import 'dart:developer';
+
+foo() async { }
+
+doAsync(stop) async {
+  if (stop) debugger();
+  await foo(); // Line 15.
+  await foo(); // Line 16.
+  await foo(); // Line 17.
+  return null;
+}
+
+testMain() {
+  // With two runs of doAsync floating around, async step should only cause
+  // us to stop in the run we started in.
+  doAsync(false);
+  doAsync(true);
+}
+
+
+asyncStep(Isolate isolate) async {
+  var event = isolate.pauseEvent;
+  expect(event, isNotNull);
+
+  // 1. Set breakpoint for the continuation and resume the isolate.
+  Instance continuation = event.asyncContinuation;
+  print("Async continuation is $continuation");
+  expect(continuation.isClosure, isTrue);
+
+  var bpt = await isolate.addBreakOnActivation(continuation);
+  expect(bpt is Breakpoint, isTrue);
+  print("Async step to $bpt");
+
+  await isolate.resume();
+  await hasStoppedAtBreakpoint(isolate);
+
+  // 2. Step past the state-machine dispatch.
+  await isolate.stepOver();
+  await hasStoppedAtBreakpoint(isolate);
+}
+
+var tests = [
+  hasStoppedAtBreakpoint,
+  stoppedAtLine(15),
+  asyncStep,
+  stoppedAtLine(16),
+  asyncStep,
+  stoppedAtLine(17),
+  resumeIsolate,
+];
+
+main(args) => runIsolateTests(args, tests, testeeConcurrent: testMain);