pkg/unittest: give Configuration a default (blank) implementation

pkg/unittest/test/unittest_test_utils.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.
 
 part of unittestTest;
 
 Future _defer(void fn()) {
   return new Future.sync(fn);
 }
 
@@ skipping 15 matching lines @@
     totalTests = results.length;
     for (var i = 0; i < results.length; i++) {
       testDetails.write(':${results[i].description}:'
           '${collapseWhitespace(results[i].message)}');
     }
   }
   return '$passed:$failed:$errors:$totalTests:$count:'
       '$setup:$teardown:$uncaughtError$testDetails';
 }
 
-class TestConfiguration extends SimpleConfiguration {
+class TestConfiguration extends Configuration {
 
   // Some test state that is captured.
   int count = 0; // A count of callbacks.
   String setup = ''; // The name of the test group setup function, if any.
   String teardown = ''; // The name of the group teardown function, if any.
 
   // The port to communicate with the parent isolate
   final SendPort _port;
   String _result;
 
-  TestConfiguration(this._port);
-
-  void onInit() {}
+  TestConfiguration(this._port) : super.blank();
 
   void onSummary(int passed, int failed, int errors, List<TestCase> results,
       String uncaughtError) {
     _result = buildStatusString(passed, failed, errors, results,
         count: count, setup: setup, teardown: teardown,
         uncaughtError: uncaughtError);
   }
 
   void onDone(bool success) {
     _port.send(_result);
@@ skipping 28 matching lines @@
   });
 }
 
 main() {
   spawnFunction(runTestInIsolate)
       .call('')
       .then((String msg) {
         expect(msg.trim(), equals(expected));
       });
 }