Add browser-compatible version.

test/loader_data_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 27 matching lines @@
         await bytes.forEach(buffer.addAll);
         expect(buffer, encoding.encode(content));
       });
     });
   }
   testFile(LATIN1, true);
   testFile(LATIN1, false);
   testFile(UTF8, true);
   testFile(UTF8, false);
 }