pkg/unittest: fixed deprecations in alt configs

pkg/unittest/lib/compact_vm_config.dart

 // Copyright (c) 2013, 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.
 
 /**
  * A test configuration that generates a compact 1-line progress bar. The bar is
  * updated in-place before and after each test is executed. If all test pass,
  * you should only see a couple lines in the terminal. If a test fails, the
  * failure is shown and the progress bar continues to be updated below it.
  */
@@ skipping 103 matching lines @@
     // Pad the rest of the line so that it looks erased.
     len = buffer.length - nonVisible - _NONE.length;
     if (len > _lastLength) {
       _lastLength = len;
     } else {
       while (len < _lastLength) {
         buffer.write(' ');
         _lastLength--;
       }
     }
-    stdout.addString(buffer.toString());
+    stdout.write(buffer.toString());
   }
 
   String _padTime(int time) =>
     (time == 0) ? '00' : ((time < 10) ? '0$time' : '$time');
 
   String _timeString(Duration duration) {
     var min = duration.inMinutes;
     var sec = duration.inSeconds % 60;
     return '${_padTime(min)}:${_padTime(sec)}';
   }
@@ skipping 32 matching lines @@
       res = res.substring(firstSpace);
     }
     return '...$res';
   }
 }
 
 void useCompactVMConfiguration() {
   if (config != null) return;
   configure(new CompactVMConfiguration());
 }