Make Dart test scripts work for the VM on Windows.

tools/testing/dart/test_options.dart

 // Copyright (c) 2011, 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("test_options_parser");
 
 List<String> defaultTestSelectors =
     const ['samples', 'standalone', 'corelib', 'co19', 'language',
            'isolate', 'stub-generator', 'vm'];
 
@@ skipping 180 matching lines @@
     
     return _expandConfigurations(configuration);
   }
 
 
   /**
    * Recursively expand a configuration with multiple values per key
    * into a list of configurations with exactly one value per key.
    */
   List<Map> _expandConfigurations(Map configuration) {
+
+    // TODO(ager): Get rid of this. This is for backwards
+    // compatibility with the python test scripts. They use system
+    // 'win32' for Windows.
+    if (configuration['system'] == 'windows') {
+      configuration['system'] = 'win32';
+    }
+
     // Expand the pseudo-values such as 'all'.
     if (configuration['architecture'] == 'all') {
       configuration['architecture'] = 'ia32,x64,simarm';
     }
     if (configuration['mode'] == 'all') {
       configuration['mode'] = 'debug,release';
     }
     if (configuration['component'] == 'most') {
       configuration['component'] = 'vm,dartc';
     }
@@ skipping 122 matching lines @@
       if (option.keys.some((key) => key == name)) {
         return option;
       }
     }
     return null;
   }
 
 
   List<_TestOptionSpecification> _options;
 }