Fix DiffProgressIndicator to use the correct parameter name

tools/testing/dart/test_progress.dart

 // Copyright (c) 2012, 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("test_runner.dart");
 #import("test_suite.dart");
 
@@ skipping 391 matching lines @@
   void _printFailureOutput(TestCase test) {
     String status = '${test.displayName}: ${test.output.result}';
     List<String> configs =
         statusToConfigs.putIfAbsent(status, () => <String>[]);
     configs.add(test.configurationString);
   }
 
   String _extractRuntime(String configuration) {
     // Extract runtime from a configuration, for example,
     // 'none-vm-checked release_ia32'.
-    List<String> runtime = config.split(' ')[0].split('-');
+    List<String> runtime = configuration.split(' ')[0].split('-');
     return '${runtime[0]}-${runtime[1]}';
   }
 
   void _printFailureSummary() {
     Map<String, List<String>> groupedStatuses = new Map<String, List<String>>();
     statusToConfigs.forEach((String status, List<String> configs) {
       Map<String, List<String>> runtimeToConfiguration =
           new Map<String, List<String>>();
       for (String config in configs) {
         String runtime = _extractRuntime(config);
@@ skipping 15 matching lines @@
       print('');
       print('$config:');
       statuses.sort((a, b) => a.compareTo(b));
       for (String status in statuses) {
         print('  $status');
       }
     });
     _printStatus();
   }
 }