Refactor groups to pipe them through to the runner.

lib/src/backend/metadata.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.
 
 library test.backend.metadata;
 
 import 'dart:collection';
 
-import '../backend/operating_system.dart';
-import '../backend/test_platform.dart';
 import '../frontend/skip.dart';
 import '../frontend/timeout.dart';
 import '../utils.dart';
+import 'operating_system.dart';
 import 'platform_selector.dart';
+import 'test_platform.dart';
 
 /// Metadata for a test or test suite.
 ///
 /// This metadata comes from declarations on the test itself; it doesn't include
 /// configuration from the user.
 class Metadata {
   /// The selector indicating which platforms the suite supports.
   final PlatformSelector testOn;
 
   /// The modification to the timeout for the test or suite.
@@ skipping 175 matching lines @@
   _serializeTimeout(Timeout timeout) {
     if (timeout == Timeout.none) return 'none';
     return {
       'duration': timeout.duration == null
           ? null
           : timeout.duration.inMicroseconds,
       'scaleFactor': timeout.scaleFactor
     };
   }
 }