Added find-shard to bot.dart.

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");
-        }
-      }
-    }
-  }
-}