Fix windows tests.

tests/standalone/io/windows_environment_script.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.
 
 import "dart:io";
 
 main() {
   var scriptDir = Platform.environment['SCRIPTDIR'];
-  Expect.isTrue(scriptDir.contains('å'));
+  if (!scriptDir.contains('å')) throw "scriptDir not containing character å";
   scriptDir = Platform.environment['ScriptDir'];
-  Expect.isTrue(scriptDir.contains('å'));
+  if (!scriptDir.contains('å')) throw "scriptDir not containing character å";
   var str = new File('$scriptDir/funky.bat').readAsStringSync();
-  Expect.isTrue(str.contains('%~dp0'));
+  if (!str.contains('%~dp0')) throw "str not containing dp0";
 }