Make the ConsoleSink call methos argument optional.

sdk/lib/io/console.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;
 
 Console _console;
 
 Console get console {
   if (_console == null) {
@@ skipping 33 matching lines @@
  * This class has a call method so you can call it directly. Calling
  * it directly is the same as calling its `writeln` method.
  */
 class ConsoleSink implements Sink<List<int>>, StringSink {
   IOSink _sink;
 
   ConsoleSink._(int fd) {
     _sink = new IOSink(new _ConsoleConsumer(fd));
   }
 
-  void call(Object message) => _sink.writeln(message);
+  void call([Object message = ""]) => _sink.writeln(message);
 
   void add(List<int> data) => _sink.add(data);
 
   void close() {}
 
   void write(Object obj) => _sink.write(obj);
 
   void writeAll(Iterable objects, [String separator=""]) =>
       _sink.writeAll(objects, separator);
 
@@ skipping 23 matching lines @@
         onDone: completer.complete,
         cancelOnError: true);
     return completer.future;
   }
 
   Future close() {
     _file.closeSync();
     return new Future.value();
   }
 }