Change Duration to take proper named optional parameters.

pkg/unittest/test_case.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.
 
 /**
  * testcase.dart: this file is sourced by unittest.dart. It defines [TestCase]
  * and assumes unittest defines the type [TestFunction].
  */
 
 /** Summarizes information about a single test case. */
@@ skipping 68 matching lines @@
       runningTime = null;
       test();
     }
   }
 
   void _complete() {
     if (runningTime == null) {
       // TODO(gram): currently the duration measurement code is blocked
       // by issue 4437. When that is fixed replace the line below with:
       //    runningTime = new Date.now().difference(startTime);
-      runningTime = new Duration(milliseconds:0);
+      runningTime = new Duration(milliseconds: 0);

[bakster, 2012/09/13 09:00:01]

How about introducing a static or a named constructor:
   Duration.empty
instead of using:
   new Duration() and 
   new new Duration(milliseconds: 0)

[kasperl, 2012/09/13 09:04:47]

That's fine but that extra constructor will not make it impossible to use new
Duration() or new Duration(milliseconds: 0), right? Unless we start adding some
kind of weird constraint that you have to pass at least one named argument
somehow.

[Lasse Reichstein Nielsen, 2012/09/13 09:30:46]

Not prevent it, but perhaps it will preempt it by being the better alternative.
E.g.:
 Duration.zero() : this(milliseconds: 0); 
This is more readable, so people will hopefully prefer to use it.

     }
     if (!_doneTeardown) {
       if (_tearDown != null) {
         _tearDown();
       }
       _doneTeardown = true;
     }
     _config.onTestResult(this);
   }
 
@@ skipping 17 matching lines @@
     }
   }
 
   void error(String messageText, String stack) {
     result = _ERROR;
     message = messageText;
     stackTrace = stack;
     _complete();
   }
 }