Add method flush to output stream

runtime/bin/http_impl.dart

 // Copyright (c) 2012, 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.
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders() : _headers = new Map<String, List<String>>();
 
   List<String> operator[](String name) {
     name = name.toLowerCase();
     return _headers[name];
@@ skipping 1086 matching lines @@
   void set onError(void callback(e)) {
     _requestOrResponse._streamSetErrorHandler(callback);
   }
 
   int _readInto(List<int> buffer, int offset, int len) {
     int result = _requestOrResponse._streamReadInto(buffer, offset, len);
     _checkScheduleCallbacks();
     return result;
   }
 
+  void flush() {
+    // Nothing to do on a HTTP output stream.
+  }
+
   void _close() {
     // TODO(sgjesse): Handle this.
   }
 
   void _dataReceived() {
     super._dataReceived();
   }
 
   _HttpRequestResponseBase _requestOrResponse;
 }
@@ skipping 979 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }