Don't create lower-case copies of already lower-case header names, in http parser.

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>>();
 
   List<String> operator[](String name) {
     name = name.toLowerCase();
     return _headers[name];
   }
 
   String value(String name) {
     name = name.toLowerCase();
     List<String> values = _headers[name];
     if (values == null) return null;
     if (values.length > 1) {
       throw new HttpException("More than one value for header $name");
     }
     return values[0];
   }
 
   void add(String name, value) {
     _checkMutable();
+    var lowerCaseName = name.toLowerCase();
     if (value is List) {
       for (int i = 0; i < value.length; i++) {
-        _add(name, value[i]);
+        _add(lowerCaseName, value[i]);
       }
     } else {
-      _add(name, value);
+      _add(lowerCaseName, value);
     }
   }
 
   void set(String name, Object value) {
     name = name.toLowerCase();
     _checkMutable();
     removeAll(name);
     add(name, value);
   }
 
@@ skipping 156 matching lines @@
     } else {
       return null;
     }
   }
 
   void set contentType(ContentType contentType) {
     _checkMutable();
     _set(HttpHeaders.CONTENT_TYPE, contentType.toString());
   }
 
+  // [name] must be a lower-case version of the name.
   void _add(String name, value) {
-    var lowerCaseName = name.toLowerCase();
     // TODO(sgjesse): Add immutable state throw HttpException is immutable.
-    if (lowerCaseName == HttpHeaders.CONTENT_LENGTH) {
+    if (name == HttpHeaders.CONTENT_LENGTH) {
       if (value is int) {
         contentLength = value;
       } else if (value is String) {
         contentLength = int.parse(value);
       } else {
         throw new HttpException("Unexpected type for header named $name");
       }
-    } else if (lowerCaseName == HttpHeaders.TRANSFER_ENCODING) {
+    } else if (name == HttpHeaders.TRANSFER_ENCODING) {
       if (value == "chunked") {
         chunkedTransferEncoding = true;
       } else {
-        _addValue(lowerCaseName, value);
+        _addValue(name, value);
       }
-    } else if (lowerCaseName == HttpHeaders.DATE) {
+    } else if (name == HttpHeaders.DATE) {
       if (value is DateTime) {
         date = value;
       } else if (value is String) {
         _set(HttpHeaders.DATE, value);
       } else {
         throw new HttpException("Unexpected type for header named $name");
       }
-    } else if (lowerCaseName == HttpHeaders.EXPIRES) {
+    } else if (name == HttpHeaders.EXPIRES) {
       if (value is DateTime) {
         expires = value;
       } else if (value is String) {
         _set(HttpHeaders.EXPIRES, value);
       } else {
         throw new HttpException("Unexpected type for header named $name");
       }
-    } else if (lowerCaseName == HttpHeaders.IF_MODIFIED_SINCE) {
+    } else if (name == HttpHeaders.IF_MODIFIED_SINCE) {
       if (value is DateTime) {
         ifModifiedSince = value;
       } else if (value is String) {
         _set(HttpHeaders.IF_MODIFIED_SINCE, value);
       } else {
         throw new HttpException("Unexpected type for header named $name");
       }
-    } else if (lowerCaseName == HttpHeaders.HOST) {
+    } else if (name == HttpHeaders.HOST) {
       if (value is String) {
         int pos = value.indexOf(":");
         if (pos == -1) {
           _host = value;
           _port = HttpClient.DEFAULT_HTTP_PORT;
         } else {
           if (pos > 0) {
             _host = value.substring(0, pos);
           } else {
             _host = null;
           }
           if (pos + 1 == value.length) {
             _port = HttpClient.DEFAULT_HTTP_PORT;
           } else {
             try {
               _port = int.parse(value.substring(pos + 1));
             } on FormatException catch (e) {
               _port = null;
             }
           }
         }
         _set(HttpHeaders.HOST, value);
       } else {
         throw new HttpException("Unexpected type for header named $name");
       }
-    } else if (lowerCaseName == HttpHeaders.CONTENT_TYPE) {
+    } else if (name == HttpHeaders.CONTENT_TYPE) {
       _set(HttpHeaders.CONTENT_TYPE, value);
     } else {
-      _addValue(lowerCaseName, value);
+      _addValue(name, value);
     }
   }
 
   void _addValue(String name, Object value) {
     List<String> values = _headers[name];
     if (values == null) {
       values = new List<String>();
       _headers[name] = values;
     }
     if (value is DateTime) {
@@ skipping 536 matching lines @@
   void clear() {
     throw new UnsupportedError("Cannot modify an unmodifiable map");
   }
   void forEach(void f(K key, V value)) => _map.forEach(f);
   Iterable<K> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
 }