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

sdk/lib/io/mime_multipart_parser.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.
 
 part of dart.io;
 
 /**
  * Parser for MIME multipart types of data as described in RFC 2046
  * section 5.1.1. The data to parse is supplied through the [:update:]
  * method. As the data is parsed the following callbacks are called:
@@ skipping 145 matching lines @@
             partEnd(false);
           }
           _state = _HEADER_START;
           break;
 
         case _HEADER_START:
           if (byte == _CharCode.CR) {
             _state = _HEADER_ENDING;
             } else {
               // Start of new header field.
-              _headerField.addCharCode(_toLowerCase(byte));
+              _headerField.writeCharCode(_toLowerCase(byte));
               _state = _HEADER_FIELD;
             }
             break;
 
           case _HEADER_FIELD:
             if (byte == _CharCode.COLON) {
               _state = _HEADER_VALUE_START;
             } else {
               if (!_isTokenChar(byte)) {
                 throw new MimeParserException("Invalid header field name");
               }
-              _headerField.addCharCode(_toLowerCase(byte));
+              _headerField.writeCharCode(_toLowerCase(byte));
             }
             break;
 
           case _HEADER_VALUE_START:
             if (byte == _CharCode.CR) {
               _state = _HEADER_VALUE_FOLDING_OR_ENDING;
             } else if (byte != _CharCode.SP && byte != _CharCode.HT) {
               // Start of new header value.
-              _headerValue.addCharCode(byte);
+              _headerValue.writeCharCode(byte);
               _state = _HEADER_VALUE;
             }
             break;
 
           case _HEADER_VALUE:
             if (byte == _CharCode.CR) {
               _state = _HEADER_VALUE_FOLDING_OR_ENDING;
             } else {
-              _headerValue.addCharCode(byte);
+              _headerValue.writeCharCode(byte);
             }
             break;
 
           case _HEADER_VALUE_FOLDING_OR_ENDING:
             _expect(byte, _CharCode.LF);
             _state = _HEADER_VALUE_FOLD_OR_END;
             break;
 
           case _HEADER_VALUE_FOLD_OR_END:
             if (byte == _CharCode.SP || byte == _CharCode.HT) {
               _state = _HEADER_VALUE_START;
             } else {
               String headerField = _headerField.toString();
               String headerValue =_headerValue.toString();
               if (headerReceived != null) {
                 headerReceived(headerField, headerValue);
               }
-              _headerField.clear();
-              _headerValue.clear();
+              _headerField = new StringBuffer();
+              _headerValue = new StringBuffer();
               if (byte == _CharCode.CR) {
                 _state = _HEADER_ENDING;
               } else {
                 // Start of new header field.
-                _headerField.addCharCode(_toLowerCase(byte));
+                _headerField.writeCharCode(_toLowerCase(byte));
                 _state = _HEADER_FIELD;
               }
             }
             break;
 
           case _HEADER_ENDING:
             _expect(byte, _CharCode.LF);
             if (headersComplete != null) headersComplete();
             _state = _CONTENT;
             contentStartIndex = index + 1;
@@ skipping 93 matching lines @@
   Function partDataReceived;
   Function partEnd;
 }
 
 
 class MimeParserException implements Exception {
   const MimeParserException([String this.message = ""]);
   String toString() => "MimeParserException: $message";
   final String message;
 }