Mark periodic4-test as flaky and add debug information.

tests/lib/async/stream_periodic4_test.dart

 // Copyright (c) 2013, 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 merging streams.
 library dart.test.stream_from_iterable;
 
 import "dart:async";
 import '../../../pkg/unittest/lib/unittest.dart';
 
+int iteration = 0;
+
 void runTest(period, maxElapsed, pauseDuration) {
+  print("Iteration: $iteration");
+  var myIteration = iteration;
+  iteration++;
+
   Function done = expectAsync0(() { });
 
   Stopwatch watch = new Stopwatch()..start();
   Stream stream = new Stream.periodic(period, (x) => x);
   var subscription;
   subscription = stream.take(5).listen((i) {
     if (watch.elapsed > maxElapsed) {
       // Test failed in this configuration. Try with more time (or give up
       // if we reached an unreasonable maxElapsed).
       if (maxElapsed > const Duration(seconds: 2)) {
         // Give up.
         expect(true, false);
       } else {
         subscription.cancel();
+        print("Cancelling subscription of iteration: $myIteration");
         // Call 'done' ourself, since it won't be invoked in the onDone handler.
         runTest(period * 2, maxElapsed * 2, pauseDuration * 2);
+        print("Invoking done of iteration inside listener: $myIteration");
         done();
         return;
       }
     }
     watch.reset();
     if (i == 2) {
       subscription.pause();
       watch.stop();
       new Timer(pauseDuration, () {
         watch.start();
         subscription.resume();
       });
     }
-  }, onDone: done);
+  }, onDone: () {
+    print("Invoking done of iteration: $myIteration");
+    done();
+  });
 }
 
 main() {
   test("stream-periodic4", () {
     runTest(const Duration(milliseconds: 2),
             const Duration(milliseconds: 8),
             const Duration(milliseconds: 10));
   });
 }