Catch errors on directory listings.

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 291 matching lines @@
     return path;
   }
 
   void allDone() {
     var count = 0;
     var systemTempDir = _tempDir();
     var lister = new Directory.fromPath(systemTempDir).list().listen(
         (FileSystemEntity fse) {
           if (fse is Directory) count++;
         },
+        onError: (error) {
+          DebugLogger.warning("Could not list temp directories, got: $error");
+        },
         onDone: () {
           if (count > MIN_NUMBER_OF_TEMP_DIRS) {
             DebugLogger.warning("There are ${count} directories "
                                 "in the system tempdir ('$systemTempDir')! "
                                 "Maybe left over directories?\n");
       }
     });
   }
 }
 
@@ skipping 189 matching lines @@
         print('@@@BUILD_STEP $stepName failures@@@');
       }
       for (String line in _failureSummary) {
         print(line);
       }
       print('');
     }
     print(_buildSummaryEnd(_failedTests));
   }
 }