Refactor handling of Transfer-Encoding

sdk/lib/io/http_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;
 
 // Global constants.
 class _Const {
   // Bytes for "HTTP".
   static const HTTP = const [72, 84, 84, 80];
@@ skipping 406 matching lines @@
               } else {
                 // Start of new header field.
                 _headerField.add(_toLowerCase(byte));
                 _state = _State.HEADER_FIELD;
               }
             }
             break;
 
           case _State.HEADER_ENDING:
             _expect(byte, _CharCode.LF);
+            _headers._mutable = false;
 
             _contentLength = _headers.contentLength;
             // Ignore the Content-Length header if Transfer-Encoding
             // is chunked (RFC 2616 section 4.4)
             if (_chunked) _contentLength = -1;
 
             // If a request message has neither Content-Length nor
             // Transfer-Encoding the message must not have a body (RFC
             // 2616 section 4.3).
             if (_messageType == _MessageType.REQUEST &&
@@ skipping 347 matching lines @@
   Function error;
   Function closed;
 }
 
 
 class HttpParserException implements Exception {
   const HttpParserException([String this.message = ""]);
   String toString() => "HttpParserException: $message";
   final String message;
 }