Slightly speed up http-parser and http-header-writing.

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 378 matching lines @@
   int _write(Uint8List buffer, int offset) {
     void write(List<int> bytes) {
       int len = bytes.length;
       for (int i = 0; i < len; i++) {
         buffer[offset + i] = bytes[i];
       }
       offset += len;
     }
 
     // Format headers.
-    _headers.forEach((String name, List<String> values) {
+    for (String name in _headers.keys) {
+      List<String> values = _headers[name];
       bool fold = _foldHeader(name);
       var nameData = name.codeUnits;
       write(nameData);
-      write(const [_CharCode.COLON, _CharCode.SP]);
+      buffer[offset++] = _CharCode.COLON;
+      buffer[offset++] = _CharCode.SP;
       for (int i = 0; i < values.length; i++) {
         if (i > 0) {
           if (fold) {
-            write(const [_CharCode.COMMA, _CharCode.SP]);
+            buffer[offset++] = _CharCode.COMMA;
+            buffer[offset++] = _CharCode.SP;
           } else {
-            write(const [_CharCode.CR, _CharCode.LF]);
+            buffer[offset++] = _CharCode.CR;
+            buffer[offset++] = _CharCode.LF;
             write(nameData);
-            write(const [_CharCode.COLON, _CharCode.SP]);
+            buffer[offset++] = _CharCode.COLON;
+            buffer[offset++] = _CharCode.SP;
           }
         }
         write(values[i].codeUnits);
       }
-      write(const [_CharCode.CR, _CharCode.LF]);
-    });
+      buffer[offset++] = _CharCode.CR;
+      buffer[offset++] = _CharCode.LF;
+    }
     return offset;
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     _headers.forEach((String name, List<String> values) {
       sb..write(name)..write(": ");
       bool fold = _foldHeader(name);
       for (int i = 0; i < values.length; i++) {
         if (i > 0) {
@@ skipping 421 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;
 }