Make HTTP headers use a growing buffer, not a fixed-size 8K one.

tests/standalone/io/http_client_request_test.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.
 
 import "dart:async";
 import "dart:io";
 import "dart:typed_data";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
@@ skipping 90 matching lines @@
     request.add([0]);
     request.close();
     request.done.catchError((error) {
       asyncEnd();
     }, test: (e) => e is HttpException);
     return request.done;
   });
 }
 
 
-void testBadHeaders() {
-  asyncStart();
-  testClientRequest((request) {
-    var value = "a";
-    for (int i = 0; i < 8 * 1024; i++) {
-      value += 'a';
-    }
-    request.headers.set('name', value);
-    request.done.catchError((error) {
-      asyncEnd();
-    }, test: (e) => e is HttpException);
-    return request.close();
-  });
-}
-
-
 void main() {
   testResponseDone();
   testBadResponseAdd();
   testBadResponseClose();
-  testBadHeaders();
 }