Update test scripts to deal with current VM behavior on optional constructor arguments.

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'];
 
 /**
  * Specification of a single test option.
  *
  * The name of the specification is used as the key for the option in
  * the Map returned from the [TestOptionParser] parse method.
  */
 class _TestOptionSpecification {
   _TestOptionSpecification(this.name,
                            this.description,
                            this.keys,
                            this.values,
                            this.defaultValue,
-                           [this.type = 'string']);
+                           [type = 'string']) : this.type = type;
   String name;
   String description;
   List<String> keys;
   List<String> values;
   var defaultValue;
   String type;
 }
 
 
 /**
@@ skipping 307 matching lines @@
       if (option.keys.some((key) => key == name)) {
         return option;
       }
     }
     return null;
   }
 
 
   List<_TestOptionSpecification> _options;
 }