Don't change the case of cookie names and values

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 {
   _HttpHeaders(String this.protocolVersion)
       : _headers = new Map<String, List<String>>();
 
@@ skipping 397 matching lines @@
          index++;
         }
       }
 
       String parseName() {
         int start = index;
         while (!done()) {
           if (s[index] == " " || s[index] == "\t" || s[index] == "=") break;
           index++;
         }
-        return s.substring(start, index).toLowerCase();
+        return s.substring(start, index);
       }
 
       String parseValue() {
         int start = index;
         while (!done()) {
           if (s[index] == " " || s[index] == "\t" || s[index] == ";") break;
           index++;
         }
-        return s.substring(start, index).toLowerCase();
+        return s.substring(start, index);
       }
 
       void expect(String expected) {
         if (done()) {
           throw new HttpException("Failed to parse header value [$s]");
         }
         if (s[index] != expected) {
           throw new HttpException("Failed to parse header value [$s]");
         }
         index++;
@@ skipping 224 matching lines @@
     int index = 0;
 
     bool done() => index == s.length;
 
     String parseName() {
       int start = index;
       while (!done()) {
         if (s[index] == "=") break;
         index++;
       }
-      return s.substring(start, index).trim().toLowerCase();
+      return s.substring(start, index).trim();
     }
 
     String parseValue() {
       int start = index;
       while (!done()) {
         if (s[index] == ";") break;
         index++;
       }
-      return s.substring(start, index).trim().toLowerCase();
+      return s.substring(start, index).trim();
     }
 
     void expect(String expected) {
       if (done()) throw new HttpException("Failed to parse header value [$s]");
       if (s[index] != expected) {
         throw new HttpException("Failed to parse header value [$s]");
       }
       index++;
     }
 
@@ skipping 79 matching lines @@
 
   String name;
   String value;
   DateTime expires;
   int maxAge;
   String domain;
   String path;
   bool httpOnly = false;
   bool secure = false;
 }