Rename XMLHttpRequest to HttpRequest.

tests/html/xhr_cross_origin_test.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('XHRCrossOriginTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 #import('dart:json');
 
 main() {
   useHtmlConfiguration();
 
   test('XHR Cross-domain', () {
-    var xhr = new XMLHttpRequest();
+    var xhr = new HttpRequest();
     var url = "https://code.google.com/feeds/issues/p/dart/issues/full?alt=json";
     xhr.open('GET', url, true);
     var validate = expectAsync1((data) {
       expect(data, contains('feed'));
       expect(data['feed'], contains('entry'));
       expect(data is Map, isTrue);
     });
     xhr.on.readyStateChange.add((e) {
       guardAsync(() {
-        if (xhr.readyState == XMLHttpRequest.DONE) {
+        if (xhr.readyState == HttpRequest.DONE) {
           validate(JSON.parse(xhr.response));
         }
       });
     });
     xhr.send();
   });
 
   test('XHR.get Cross-domain', () {
     var url = "https://code.google.com/feeds/issues/p/dart/issues/full?alt=json";
-    new XMLHttpRequest.get(url, expectAsync1((xhr) {
+    new HttpRequest.get(url, expectAsync1((xhr) {
       var data = JSON.parse(xhr.response);
       expect(data, contains('feed'));
       expect(data['feed'], contains('entry'));
       expect(data is Map, isTrue);
     }));
   });
 }