create_shard_data.dart now generates `dartfmt` style output.

tools/gardening/bin/create_shard_groups.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.
 
 // Outputs source code for `part` used by `shard2group.dart`. Usage:
 // `dart bin/create_shard_groups.dart source.html >lib/src/shard_data.dart`.
 
 import 'dart:io';
 import 'dart:math' as math;
 
@@ skipping 71 matching lines @@
   // Print the resulting Dart declaration.
   print("""
 // 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.
 //
 // ----- Generated by create_shard_groups.dart, do not edit! -----
 
 part of gardening.shard2group;
 
-const Map<String, List<String>> shardGroups = const {
-""");
+const Map<String, List<String>> shardGroups = const {""");
   for (int i = 0; i < groupCount; i++) {
     print("  '${groups[i]}': const <String>[");
     for (String shard in shards[i]) {
       print("    '$shard',");
     }
     print("  ],");
   }
   print('};');
 }