Only lower-case ContentType's values if the name is 'charset'.

sdk/lib/io/http_headers.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;
 
 class _HttpHeaders implements HttpHeaders {
   final Map<String, List<String>> _headers;
   final String protocolVersion;
 
@@ skipping 729 matching lines @@
       }
 
       while (!done()) {
         skipWS();
         if (done()) return;
         String name = parseParameterName();
         skipWS();
         expect("=");
         skipWS();
         String value = parseParameterValue();
+        if (name == 'charset' && this is _ContentType) {
+          // Charset parameter of ContentTypes are always lower-case.
+          value = value.toLowerCase();
+        }
         parameters[name] = value;
         skipWS();
         if (done()) return;
         expect(parameterSeparator);
       }
     }
 
     skipWS();
     _value = parseValue();
     skipWS();
@@ skipping 12 matching lines @@
                String subType,
                String charset,
                Map<String, String> parameters)
       : _primaryType = primaryType, _subType = subType, super("") {
     if (_primaryType == null) _primaryType = "";
     if (_subType == null) _subType = "";
     _value = "$_primaryType/$_subType";
     if (parameters != null) {
       _ensureParameters();
       parameters.forEach((String key, String value) {
-        this._parameters[key.toLowerCase()] = value.toLowerCase();
+        String lowerCaseKey = key.toLowerCase();
+        if (lowerCaseKey == "charset") {
+          value = value.toLowerCase();
+        }
+        this._parameters[lowerCaseKey] = value;
       });
     }
     if (charset != null) {
       _ensureParameters();
       this._parameters["charset"] = charset.toLowerCase();
     }
   }
 
   _ContentType._();
 
@@ skipping 169 matching lines @@
             (codeUnit >= 0x23 && codeUnit <= 0x2B) ||
             (codeUnit >= 0x2D && codeUnit <= 0x3A) ||
             (codeUnit >= 0x3C && codeUnit <= 0x5B) ||
             (codeUnit >= 0x5D && codeUnit <= 0x7E))) {
         throw new FormatException(
             "Invalid character in cookie value, code unit: '$codeUnit'");
       }
     }
   }
 }