Use a sync-writing StreamConsumer for stdout/stderr.

sdk/lib/io/stdio.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;
 
 const int _STDIO_HANDLE_TYPE_TERMINAL = 0;
 const int _STDIO_HANDLE_TYPE_PIPE = 1;
 const int _STDIO_HANDLE_TYPE_FILE = 2;
 const int _STDIO_HANDLE_TYPE_SOCKET = 3;
@@ skipping 184 matching lines @@
   final OSError osError;
 
   const StdoutException(this.message, [this.osError]);
 
   String toString() {
     return "StdoutException: $message${osError == null ? "" : ", $osError"}";
   }
 }
 
 
+class _StdConsumer implements StreamConsumer<List<int>> {
+  final _file;
+
+  _StdConsumer(int fd) : _file = _File._openStdioSync(fd);
+
+  Future addStream(Stream<List<int>> stream) {
+    var completer = new Completer();
+    var sub;
+    sub = stream.listen(
+        (data) {
+          try {
+            _file.writeFromSync(data);
+          } catch (e, s) {
+            sub.cancel();
+            completer.completeError(e, s);
+          }
+        },
+        onError: completer.completeError,
+        onDone: completer.complete,
+        cancelOnError: true);
+    return completer.future;
+  }
+
+  Future close() {
+    _file.closeSync();
+    return new Future.value();
+  }
+}
+
+
 class _StdSink implements IOSink {
   final IOSink _sink;
 
   _StdSink(this._sink);
 
   Encoding get encoding => _sink.encoding;
   void set encoding(Encoding encoding) {
     _sink.encoding = encoding;
   }
   void write(object) => _sink.write(object);
@@ skipping 87 matching lines @@
   return StdioType.OTHER;
 }
 
 
 class _StdIOUtils {
   external static _getStdioOutputStream(int fd);
   external static Stdin _getStdioInputStream();
   external static int _socketType(nativeSocket);
   external static _getStdioHandleType(int fd);
 }