Add browser-compatible version.

test/loader_http_test.dart

 // Copyright (c) 2015, 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.
 
+@TestOn("vm");
+
 import "dart:async";
 import "dart:convert";
 import "dart:io";
 
 import "package:resource/resource.dart";
 import "package:test/test.dart";
 
 const content = "Rødgrød med fløde";
 
 main() {
@@ skipping 68 matching lines @@
         }
         if (w > weight) {
           weight = w;
           encoding = e;
         }
       }
     }
   }
   return encoding;
 }