fixes #221, initial sync*, async, async* implementation

test/codegen/language/async_star_regression_23116_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.
+
+// Regression test for https://code.google.com/p/dart/issues/detail?id=23116
+
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+import 'dart:async';
+
+Stream<int> foo(Completer completer, Future future) async* {
+  completer.complete(100);
+  int x = await future;
+  Expect.equals(42, x);
+}
+
+test() async {
+  Completer completer1 = new Completer();
+  Completer completer2 = new Completer();
+  StreamSubscription s = foo(completer1, completer2.future).listen((v) => null);
+  await completer1.future;
+  // At this moment foo is waiting on the given future.
+  s.pause();
+  // Ensure that execution of foo is not resumed - the future is not completed
+  // yet.
+  s.resume();
+  completer2.complete(42);
+}
+
+main() {
+  asyncStart();
+  test().then((_) => asyncEnd());
+}