Add console to dart:io for synchronus writing to stdout and stderr

tests/standalone/io/console_script.dart

+// Copyright (c) 2014, 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.
+
+import "dart:io";
+
+void test(ConsoleSink sink) {
+  sink.add([65, 66, 67]);
+  sink.write('DEF');
+  sink.writeAll(['GH', 'I']);
+  sink.writeCharCode(74);
+  sink.writeln('KLM');
+}
+
+void main(List<String> arguments) {
+  console.log('stdout');
+  console.error('stderr');
+  test(console.log);
+  test(console.error);
+  exit(1);
+}