Fix deprecation warnings in dart:io. Now completely warning free.

sdk/lib/io/string_transformer.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;
 
 /**
  * String encodings.
  */
 class Encoding {
@@ skipping 139 matching lines @@
   controller.close();
   assert(bytes != null);
   return bytes;
 }
 
 
 class LineTransformer extends StreamEventTransformer<String, String> {
   const int _LF = 10;
   const int _CR = 13;
 
-  final StringBuffer _buffer = new StringBuffer();
+  StringBuffer _buffer = new StringBuffer();
   String _carry;
 
   void _handle(String data, StreamSink<String> sink, bool isClosing) {
     if (_carry != null) {
       data = _carry.concat(data);
       _carry = null;
     }
     int startPos = 0;
     int pos = 0;
     while (pos < data.length) {
       int skip = 0;
       int char = data.codeUnitAt(pos);
       if (char == _LF) {
         skip = 1;
       } else if (char == _CR) {
         skip = 1;
         if (pos + 1 < data.length) {
           if (data.codeUnitAt(pos + 1) == _LF) {
             skip = 2;
           }
         } else if (!isClosing) {
           _carry = data.substring(startPos);
           return;
         }
       }
       if (skip > 0) {
-        _buffer.add(data.substring(startPos, pos));
+        _buffer.write(data.substring(startPos, pos));
         sink.add(_buffer.toString());
-        _buffer.clear();
+        _buffer = new StringBuffer();
         startPos = pos = pos + skip;
       } else {
         pos++;
       }
     }
     if (pos != startPos) {
       // Add remaining
-      _buffer.add(data.substring(startPos, pos));
+      _buffer.write(data.substring(startPos, pos));
     }
     if (isClosing && !_buffer.isEmpty) {
       sink.add(_buffer.toString());
-      _buffer.clear();
+      _buffer = new StringBuffer();
     }
   }
 
   void handleData(String data, StreamSink<String> sink) {
     _handle(data, sink, false);
   }
 
   void handleDone(StreamSink<String> sink) {
     _handle("", sink, true);
     sink.close();
@@ skipping 94 matching lines @@
 
 // Utility class for decoding Windows current code page data delivered
 // as a stream of bytes.
 class _WindowsCodePageDecoder extends StreamEventTransformer<List<int>, String> {
   void handleData(List<int> data, StreamSink<String> sink) {
     sink.add(_decodeBytes(data));
   }
 
   external static String _decodeBytes(List<int> bytes);
 }