Make browser tests all run from a server instead of the local filesystem.

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/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
+import 'dart:json' as json;
 
 main() {
   useHtmlConfiguration();
+  var url = "../../../../tests/html/xhr_cross_origin_data.txt";
+
+  void validate200Response(xhr) {
+    expect(xhr.status, equals(200));
+    var data = json.parse(xhr.response);
+    expect(data, contains('feed'));
+    expect(data['feed'], contains('entry'));
+    expect(data, isMap);
+  }
+
+  void validate404(xhr) {
+    expect(xhr.status, equals(404));
+    expect(xhr.responseText, equals(''));
+  }
 
   test('XHR No file', () {
     HttpRequest xhr = new HttpRequest();
     xhr.open("GET", "NonExistingFile", true);
-    xhr.on.readyStateChange.add(expectAsync1((event) {
+    xhr.on.readyStateChange.add(expectAsyncUntil1((event) {
       if (xhr.readyState == HttpRequest.DONE) {
-        expect(xhr.status, equals(0));
-        expect(xhr.responseText, equals(''));
+        validate404(xhr);
       }
-    }));
+    }, () => xhr.readyState == HttpRequest.DONE));
+    xhr.send();
+  });
+
+  test('XHR file', () {
+    var xhr = new HttpRequest();
+    xhr.open('GET', url, true);
+    xhr.on.readyStateChange.add(expectAsyncUntil1((e) {
+      if (xhr.readyState == HttpRequest.DONE) {
+        validate200Response(xhr);
+      }
+    }, () => xhr.readyState == HttpRequest.DONE));
     xhr.send();
   });
 
   test('XHR.get No file', () {
     new HttpRequest.get("NonExistingFile", expectAsync1((xhr) {
       expect(xhr.readyState, equals(HttpRequest.DONE));
-      expect(xhr.status, equals(0));
-      expect(xhr.responseText, equals(''));
+      validate404(xhr);
+    }));
+  });
+
+  test('XHR.get file', () {
+    var xhr = new HttpRequest.get(url, expectAsync1((event) {
+      expect(event.readyState, equals(HttpRequest.DONE));
+      validate200Response(event);
+    }));
+  });
+
+  test('XHR.getWithCredentials No file', () {
+    new HttpRequest.getWithCredentials("NonExistingFile", expectAsync1((xhr) {
+      expect(xhr.readyState, equals(HttpRequest.DONE));
+      validate404(xhr);
+    }));
+  });
+
+  test('XHR.getWithCredentials file', () {
+    new HttpRequest.getWithCredentials(url, expectAsync1((xhr) {
+      expect(xhr.readyState, equals(HttpRequest.DONE));
+      validate200Response(xhr);
     }));
   });
 }