Regression test for error rejecting transaction (dart-archive/async#230)

Towards dart-lang/async#229

Add a skipped test demonstrating the sequence of interaction with a
StreamQueueTransaction that leads to a `StateError` during the call to
`transaction.reject()`.

pkgs/async/test/stream_queue_test.dart

@@ -922,6 +922,25 @@ void main() {
         await flushMicrotasks();
         controller.close();
       });
+
+      test(
+          'can reject a transaction where one copy is fully consumed '
+          'in a transaction and a second copy is made', () async {
+        // Regression test for https://github.com/dart-lang/async/issues/229
+        final queue = StreamQueue(Stream.fromIterable([0]));
+        final transaction = queue.startTransaction();
+
+        final copy1 = transaction.newQueue();
+        final inner1 = copy1.startTransaction();
+        final innerCopy1 = inner1.newQueue();
+        await innerCopy1.next;
+
+        transaction.newQueue();
+
+        transaction.reject();
+        expect(await queue.next, 0);
+        expect(await queue.hasNext, isFalse);
+      }, skip: 'https://github.com/dart-lang/async/issues/229');
     });
 
     group('when committed', () {