Fix type error in test scripts

tools/testing/dart/test_progress.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.
 
 library test_progress;
 
 import "dart:io";
 import "dart:io" as io;
 import "http_server.dart" as http_server;
 import "status_file_parser.dart";
@@ skipping 292 matching lines @@
         onDone: () {
           if (count > MIN_NUMBER_OF_TEMP_DIRS) {
             DebugLogger.warning("There are ${count} directories "
                                 "in the system tempdir ('$systemTempDir')! "
                                 "Maybe left over directories?\n");
       }
     });
   }
 }
 
-class LineProgressIndicator extends EventListener {
+class LineProgressIndicator extends EventListener implements ProgressIndicator {
   void done(TestCase test) {
     var status = 'pass';
     if (test.lastCommandOutput.unexpectedOutput) {
       status = 'fail';
     }
     print('Done ${test.configurationString} ${test.displayName}: $status');
   }
 }
 
 class TestFailurePrinter extends EventListener {
@@ skipping 193 matching lines @@
         print('@@@BUILD_STEP $stepName failures@@@');
       }
       for (String line in _failureSummary) {
         print(line);
       }
       print('');
     }
     super.allDone();
   }
 }