Reapply Futureification.

tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate

 // 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.
 
 part of $LIBRARYNAME;
 
 /**
  * A utility for retrieving data from a URL.
  *
  * HttpRequest can be used to obtain data from http, ftp, and file
@@ skipping 67 matching lines @@
    */
   static Future<HttpRequest> request(String url,
       {String method, bool withCredentials, String responseType, sendData,
       void onProgress(ProgressEvent e)}) {
     var completer = new Completer<HttpRequest>();
 
     var xhr = new HttpRequest();
     if (method == null) {
       method = 'GET';
     }
-    xhr.open(method, url, true);
+    xhr.open(method, url, async: true);
 
     if (withCredentials != null) {
       xhr.withCredentials = withCredentials;
     }
 
     if (responseType != null) {
       xhr.responseType = responseType;
     }
 
     if (onProgress != null) {
@@ skipping 42 matching lines @@
 $if DART2JS
     var xhr = new HttpRequest();
     return JS('bool', '"onloadend" in #', xhr);
 $else
     return true;
 $endif
   }
 
 $!MEMBERS
 }