Use a sync-writing StreamConsumer for stdout/stderr.

sdk/lib/io/file_impl.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.
 
 part of dart.io;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 163 matching lines @@
 
 class _FileStreamConsumer extends StreamConsumer<List<int>> {
   File _file;
   Future<RandomAccessFile> _openFuture;
   StreamSubscription _subscription;
 
   _FileStreamConsumer(File this._file, FileMode mode) {
     _openFuture = _file.open(mode: mode);
   }
 
-  _FileStreamConsumer.fromStdio(int fd) {
-    assert(1 <= fd && fd <= 2);
-    _openFuture = new Future.value(_File._openStdioSync(fd));
-  }
-
   Future<File> addStream(Stream<List<int>> stream) {
     Completer<File> completer = new Completer<File>();
     _openFuture
       .then((openedFile) {
         void error(e, [StackTrace stackTrace]) {
           _subscription.cancel();
           openedFile.close();
           completer.completeError(e, stackTrace);
         }
         _subscription = stream.listen(
@@ skipping 707 matching lines @@
 
   void _checkAvailable() {
     if (_asyncDispatched) {
       throw new FileSystemException("An async operation is currently pending", path);
     }
     if (closed) {
       throw new FileSystemException("File closed", path);
     }
   }
 }