Avoid unneeded toLowerCase and add fast version of _isTokenChar, 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 {
   final Map<String, List<String>> _headers;
   final String protocolVersion;
 
@@ skipping 23 matching lines @@
     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();
+    _addAll(name.toLowerCase(), value);
+  }
+
+  void _addAll(String name, value) {
     if (value is List) {
       for (int i = 0; i < value.length; i++) {
-        _add(lowerCaseName, value[i]);
+        _add(name, value[i]);
       }
     } else {
-      _add(lowerCaseName, value);
+      _add(name, value);
     }
   }
 
   void set(String name, Object value) {
+    _checkMutable();
     name = name.toLowerCase();
-    _checkMutable();
-    removeAll(name);
-    add(name, value);
+    _headers.remove(name);
+    _addAll(name, value);
   }
 
   void remove(String name, Object value) {
     _checkMutable();
     name = name.toLowerCase();
     List<String> values = _headers[name];
     if (values != null) {
       int index = values.indexOf(value);
       if (index != -1) {
         values.removeRange(index, index + 1);
@@ skipping 266 matching lines @@
       _headers[name] = values;
     }
     if (value is DateTime) {
       values.add(HttpDate.format(value));
     } else {
       values.add(value.toString());
     }
   }
 
   void _set(String name, String value) {
-    name = name.toLowerCase();
+    assert(name == name.toLowerCase());
     List<String> values = new List<String>();
     _headers[name] = values;
     values.add(value);
   }
 
   _checkMutable() {
     if (!_mutable) throw new HttpException("HTTP headers are not mutable");
   }
 
   _updateHostHeader() {
@@ skipping 487 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;
 }