By default use current code page on Windows for decoding string

sdk/lib/io/input_stream.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Basic input stream which supplies binary data.
  *
  * Input streams are used to read data sequentially from some data
  * source. All input streams are non-blocking. They each have a number
  * of read calls which will always return without any IO related
@@ skipping 85 matching lines @@
 }
 
 
 /**
  * String encodings.
  */
 class Encoding {
   static const Encoding UTF_8 = const Encoding._internal("UTF-8");
   static const Encoding ISO_8859_1 = const Encoding._internal("ISO-8859-1");
   static const Encoding ASCII = const Encoding._internal("ASCII");
+  /**
+   * SYSTEM encoding is the current code page on Windows and UTF-8 on
+   * Linux and Mac.
+   */
+  static const Encoding SYSTEM = const Encoding._internal("SYSTEM");
   const Encoding._internal(String this.name);
   final String name;
 }
 
 
 /**
  * A string input stream wraps a basic input stream and supplies
  * string data. This data can be read either as string chunks or as
  * lines separated by line termination character sequences.
  */
@@ skipping 126 matching lines @@
   void set onError(void callback(e));
 }
 
 
 class StreamException implements Exception {
   const StreamException([String this.message = ""]);
   const StreamException.streamClosed() : message = "Stream closed";
   String toString() => "StreamException: $message";
   final String message;
 }