Fix problem occurring when an async* stream is paused at the end of a yield*.

tests/language/yieldstar_pause_test.dart

+// Copyright (c) 2016, 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.
+
+import "dart:async";
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+// Regression test for http://dartbug.com/27205
+// If a yield-star completes while the stream is paused, it didn't resume.
+
+main() async {
+  asyncStart();
+  var c = new Completer();
+  var s = yieldStream(mkStream());
+  var sub;
+  sub = s.listen((v) {
+    sub.pause();
+    print(v);
+    Timer.run(sub.resume);
+  }, onDone: () {
+    print("DONE");
+    c.complete(null);
+  });
+
+  await c.future;
+  asyncEnd();
+}
+
+Stream yieldStream(Stream s) async* {
+  yield* s;
+}
+
+Stream mkStream() {
+  var s = new StreamController(sync:true);
+  // The close event has to be sent and received between
+  // the pause and resume above.
+  // Using a sync controller and a Timer.run(sub.resume) ensures this.
+  Timer.run(() {
+    s.add("event");
+    s.close();
+  });
+  return s.stream;
+}