Rename XMLHttpRequest to HttpRequest.

samples/leap/request_cache.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.
 
 #library('request_cache');
 
 #import('dart:html');
 
 /** File system implementation using HTML5's Web Storage. */
 class HttpRequestCache {
   final Storage storage;
 
   HttpRequestCache() : storage = window.sessionStorage;
 
   String readAll(String filename) {
     String response = storage[filename];
 
     if (response == null) {
-      XMLHttpRequest xr = new XMLHttpRequest();
+      HttpRequest xr = new HttpRequest();
       xr.open("GET", filename, false);
       xr.send();
       response = xr.responseText;
       storage[filename] = response;
     }
     return response;
   }
 }