Add find_timeouts and caching to tools/gardening

tools/gardening/bin/shard2group.dart

 #!/usr/bin/env 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.
 
 // Translates a buildbot shard name to the corresponding column group name
 // on the buildbot site, such that it's easier to find the right column.
 //
 // Example: `dart bin/shard2group.dart precomp-linux-debug-x64-be`
 // prints `vm-precomp(5): precomp-linux-debug-x64-be`.
 
 library gardening.shard2group;
+
 import 'dart:io';
 part 'package:gardening/src/shard_data.dart';
 
 main(List<String> args) async {
   if (args.length == 0) {
     print('Usage: dart shard2group.dart <shard-name1> [<shard-name2> ...]');
     print('Run bin/create_shard_groups.dart to refresh shard data');
     exit(1);
   }
 
   for (String arg in args) {
     for (String group in shardGroups.keys) {
       List<String> shardGroup = shardGroups[group];
       for (int i = 0; i < shardGroup.length; i++) {
         String shard = shardGroup[i];
         if (shard.contains(arg)) {
           print("$group(${i+1}): $shard");
         }
       }
     }
   }
 }