Rename XMLHttpRequest to HttpRequest.

tests/html/xhr_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('XHRTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 #import('dart:json');
 
 main() {
   useHtmlConfiguration();
 
   test('XHR No file', () {
-    XMLHttpRequest xhr = new XMLHttpRequest();
+    HttpRequest xhr = new HttpRequest();
     xhr.open("GET", "NonExistingFile", true);
     xhr.on.readyStateChange.add(expectAsync1((event) {
-      if (xhr.readyState == XMLHttpRequest.DONE) {
+      if (xhr.readyState == HttpRequest.DONE) {
         expect(xhr.status, equals(0));
         expect(xhr.responseText, equals(''));
       }
     }));
     xhr.send();
   });
 
   test('XHR.get No file', () {
-    new XMLHttpRequest.get("NonExistingFile", expectAsync1((xhr) {
-      expect(xhr.readyState, equals(XMLHttpRequest.DONE));
+    new HttpRequest.get("NonExistingFile", expectAsync1((xhr) {
+      expect(xhr.readyState, equals(HttpRequest.DONE));
       expect(xhr.status, equals(0));
       expect(xhr.responseText, equals(''));
     }));
   });
 }