Work around issue 14971 in barback.

pkg/barback/lib/src/serialize.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.
 
 library barback.serialize;
 
 import 'dart:async';
 import 'dart:isolate';
 
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 27 matching lines @@
 
 /// Convert a [SendPort] whose opposite is waiting to send us a stream into a
 /// [Stream].
 ///
 /// No stream data will actually be sent across the isolate boundary until
 /// someone subscribes to the returned stream.
 Stream deserializeStream(SendPort sendPort) {
   return callbackStream(() {
     var receivePort = new ReceivePort();
     sendPort.send(receivePort.sendPort);
+    // TODO(nweiz): use a const constructor for StreamTransformer when issue
+    // 14971 is fixed.
     return receivePort.transform(
-        const StreamTransformer(_deserializeTransformer));
+        new StreamTransformer(_deserializeTransformer));
   });
 }
 
 /// The body of a [StreamTransformer] that deserializes the values in a stream
 /// sent by [serializeStream].
 StreamSubscription _deserializeTransformer(Stream input, bool cancelOnError) {
   var subscription;
   var transformed = input.transform(new StreamTransformer.fromHandlers(
       handleData: (data, sink) {
     if (data['type'] == 'data') {
@@ skipping 67 matching lines @@
 // short of a giant pile of type tests for each known exception type.
 //
 // So just try it. If it throws, default to toString().
 String _getErrorMessage(error) {
   try {
     return error.message;
   } on NoSuchMethodError catch (_) {
     return error.toString();
   }
 }