Update XMLHttpRequest documentation.

lib/html/doc/interface/HttpRequestProgressEvent.dartdoc

 // 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.
 
 // WARNING:
 //   This file contains documentation that is merged into the real source.
 //   Do not make code changes here.
 
 /// @domName XMLHttpRequestProgressEvent
-interface XMLHttpRequestProgressEvent extends ProgressEvent {
+interface HttpRequestProgressEvent extends ProgressEvent {
 
   /** @domName XMLHttpRequestProgressEvent.position */
   final int position;
 
   /** @domName XMLHttpRequestProgressEvent.totalSize */
   final int totalSize;
 }