Use patching for dart:io.

lib/io/string_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.
 
 // Interface for decoders decoding binary data into string data. The
 // decoder keeps track of line breaks during decoding.
 abstract class _StringDecoder {
   // 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);
@@ skipping 43 matching lines @@
 
 class DecoderException implements Exception {
   const DecoderException([String this.message]);
   String toString() => "DecoderException: $message";
   final String message;
 }
 
 
 // Utility class for decoding UTF-8 from data delivered as a stream of
 // bytes.
-class _StringDecoderBase implements _StringDecoder {
+abstract class _StringDecoderBase implements _StringDecoder {
   _StringDecoderBase()
       : _bufferList = new _BufferList(),
         _result = new List<int>(),
         _lineBreakEnds = new Queue<int>();
 
   int write(List<int> buffer) {
     _bufferList.add(buffer);
     // Decode as many bytes into characters as possible.
     while (_bufferList.length > 0) {
       if (!_processNext()) {
@@ skipping 72 matching lines @@
     _lineBreakEnds.add(charPos);
     _lineBreaks++;
   }
 
   void _resetResult() {
     _charOffset += _result.length;
     _result = new List<int>();
     _resultOffset = 0;
   }
 
-  abstract bool _processNext();
+  bool _processNext();
 
   _BufferList _bufferList;
   int _resultOffset = 0;
   List<int> _result;
   int _lineBreaks = 0;  // Number of line breaks in the current list.
   // The positions of the line breaks are tracked in terms of absolute
   // character positions from the begining of the decoded data.
   Queue<int> _lineBreakEnds;  // Character position of known line breaks.
   int _charOffset = 0;  // Character number of the first character in the list.
   int _charCount = 0;  // Total number of characters decoded.
@@ skipping 355 matching lines @@
   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?
   Timer _scheduledDataCallback;
   Timer _scheduledLineCallback;
   Timer _scheduledCloseCallback;
   Function _clientDataHandler;
   Function _clientLineHandler;
   Function _clientCloseHandler;
 }