Fix timing issue in stream_empty_test, and make analyzer expect it to pass.

tests/lib/async/stream_empty_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.
 
 // Test empty stream.
 import "package:expect/expect.dart";
 import "dart:async";
 import 'package:async_helper/async_helper.dart';
 
-main() async {
+main() {
+  asyncStart();
+  runTest().whenComplete(asyncEnd);
+}
+
+Future runTest() async {
   unreachable([a,b]) { throw "UNREACHABLE"; }
   int tick = 0;
   ticker() { tick++; }
 
   asyncStart();
 
   Stream<int> s = const Stream<int>.empty();  // Is const constructor.
   Expect.isFalse(s is Stream<String>);  // Respects type parameter.
   StreamSubscription<int> sub =
      s.listen(unreachable, onError: unreachable, onDone: ticker);
@@ skipping 28 matching lines @@
   Expect.equals(tick, 1);
   sub3.resume();
   await flushMicrotasks();
   // Now completed.
   Expect.equals(tick, 2);
 
   asyncEnd();
 }
 
 Future flushMicrotasks() => new Future.delayed(Duration.ZERO);