Initializing formals can't be optional parameters

runtime/bin/string_stream.dart

 // Copyright (c) 2011, 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.
 
 // Interface for decoders decoding binary data into objects of type T.
 interface _Decoder<T> {
   // Add more binary data to be decoded. The ownership of the buffer
   // is transfered to the decoder and the caller most not modify it any more.
   int write(List<int> buffer);
 
   // Returns whether any decoded data is available.
   bool isEmpty();
 
   // Get the data decoded since the last call to decode.
   T get decoded();
 }
 
 
 class DecoderException implements Exception {
-  const DecoderException([String this.message]);
+  const DecoderException([String msg]) : message = msg;
   String toString() => "DecoderException: $message";
   final String message;
 }
 
 
 // Utility class for decoding UTF-8 from data delivered as a stream of
 // bytes.
 class _StringDecoderBase implements _Decoder<String> {
   _StringDecoderBase()
       : _bufferList = new _BufferList(),
@@ skipping 100 matching lines @@
       // Remove the value peeked from the buffer list.
       _bufferList.next();
     }
     _result.addCharCode(value);
     return true;
   }
 }
 
 
 class _StringInputStream implements StringInputStream {
-  _StringInputStream(InputStream this._input, [String this._encoding]) {
+  _StringInputStream(InputStream this._input, [String encoding])
+      : _encoding = encoding {
     if (_encoding === null) {
       _encoding = "UTF-8";
     }
     if (_encoding == "UTF-8") {
       _decoder = new _UTF8Decoder();
     } else if (_encoding == "ISO-8859-1") {
       _decoder = new _Latin1Decoder();
     } else if (_encoding == "ASCII") {
       _decoder = new _AsciiDecoder();
     } else {
@@ skipping 161 matching lines @@
   String _encoding;
   _Decoder _decoder;
   String _buffer;  // String can be buffered here if readLine is used.
   int _bufferLineStart;  // Current offset into _buffer if any.
   bool _inputClosed = false;  // Is the underlying input stream closed?
   bool _closed = false;  // Is this stream closed.
   bool _eof = false;  // Has all data been read from the decoder?
   var _clientDataHandler;
   var _clientCloseHandler;
 }