Add an "onPlatform" parameter to test() and group().

lib/src/backend/invoker.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.invoker;
 
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 24 matching lines @@
 
   LocalTest(this.name, this.metadata, body(), {tearDown()})
       : _body = body,
         _tearDown = tearDown;
 
   /// Loads a single runnable instance of this test.
   LiveTest load(Suite suite) {
     var invoker = new Invoker._(suite, this);
     return invoker.liveTest;
   }
+
+  Test change({String name, Metadata metadata}) {
+    if (name == null) name = this.name;
+    if (metadata == null) metadata = this.metadata;
+    return new LocalTest(name, metadata, _body, tearDown: _tearDown);
+  }
 }
 
 /// The class responsible for managing the lifecycle of a single local test.
 ///
 /// The current invoker is accessible within the zone scope of the running test
 /// using [Invoker.current]. It's used to track asynchronous callbacks and
 /// report asynchronous errors.
 class Invoker {
   /// The live test being driven by the invoker.
   ///
@@ skipping 138 matching lines @@
           Timer.run(_controller.completer.complete);
         });
       },
           zoneSpecification: new ZoneSpecification(
               print: (self, parent, zone, line) => _controller.print(line)),
           zoneValues: {#test.invoker: this},
           onError: handleError);
     });
   }
 }