Improve output of current-summary gardening tool.

tools/gardening/lib/src/buildbot_data.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 import 'buildbot_structures.dart';
 import 'logdog.dart' as logdog;
 import 'util.dart';
 
 /// Data describing the steps of the buildbots.
@@ skipping 789 matching lines @@
   /// Returns the [BuildUri] corresponding to the build steps for shards in this
   /// group.
   List<BuildUri> createUris(int buildNumber, {bool includeInactive: false}) {
     List<BuildUri> uriList = <BuildUri>[];
     for (BuildSubgroup subgroup in subgroups) {
       if (!subgroup.isActive && !includeInactive) continue;
       uriList.addAll(subgroup.createUris(buildNumber));
     }
     return uriList;
   }
+
+  String toString() => groupName;
 }
 
 /// A group of buildbot subgroups, often shards, that share their test steps,
 /// for instance all `dart2js-win7-ie10chrome-*-4-be` shards.
 class BuildSubgroup {
   /// The names of the shards in this, for instance
   /// `dart2js-win7-ie10chrome-1-4-be`, `dart2js-win7-ie10chrome-2-4-be`, etc.
   final List<String> shardNames;
 
   /// The names of the test steps for the shards in this subgroup, for instance
@@ skipping 130 matching lines @@
           stepNames.add(step);
         }
       }
       if (stepNames.isNotEmpty) {
         subgroups[subgroup] = stepNames;
       }
     }
   }
   return subgroups;
 }