pkg/test: cleanup imports

lib/src/backend/group.dart

 // Copyright (c) 2015, 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 'group_entry.dart';
 import 'metadata.dart';
 import 'operating_system.dart';
-import 'group_entry.dart';
 import 'test.dart';
 import 'test_platform.dart';
 
 /// A group contains one or more tests and subgroups.
 ///
 /// It includes metadata that applies to all contained tests.
 class Group implements GroupEntry {
   final String name;
 
   final Metadata metadata;
@@ skipping 48 matching lines @@
   /// Returns the entries of this group mapped using [callback].
   ///
   /// Any `null` values returned by [callback] will be removed.
   List<GroupEntry> _map(GroupEntry callback(GroupEntry entry)) {
     return entries
         .map((entry) => callback(entry))
         .where((entry) => entry != null)
         .toList();
   }
 }