Revise barback logging patch.

pkg/barback/lib/src/utils.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.utils;
 
 import 'dart:async';
-import 'dart:io';
 
 /// A pair of values.
 class Pair<E, F> {
   E first;
   F last;
 
   Pair(this.first, this.last);
 
   String toString() => '($first, $last)';
 
@@ skipping 170 matching lines @@
     stream.listen(
         controller.add,
         onError: controller.addError,
         onDone: controller.close);
   }).catchError((e, stackTrace) {
     controller.addError(e, stackTrace);
     controller.close();
   });
   return controller.stream;
 }