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

lib/src/runner/vm/isolate_listener.dart

Index: lib/src/runner/vm/isolate_listener.dart
diff --git a/lib/src/runner/vm/isolate_listener.dart b/lib/src/runner/vm/isolate_listener.dart
index b40140e7b38d06c3736b257fcef63e575d513284..ed23a1d1adfeeb67d6fe2ff89e3fc56d0e1d3f09 100644
--- a/lib/src/runner/vm/isolate_listener.dart
+++ b/lib/src/runner/vm/isolate_listener.dart
@@ -11,6 +11,8 @@ import '../../backend/declarer.dart';
 import '../../backend/metadata.dart';
 import '../../backend/suite.dart';
 import '../../backend/test.dart';
+import '../../backend/test_platform.dart';
+import '../../util/io.dart';
 import '../../util/remote_exception.dart';
 import '../../utils.dart';
 
@@ -59,8 +61,9 @@ class IsolateListener {
       return;
     }
 
-    new IsolateListener._(new Suite(declarer.tests, metadata: metadata))
-        ._listen(sendPort);
+    var suite = new Suite(declarer.tests, metadata: metadata)
+        .forPlatform(TestPlatform.vm, os: currentOS);
+    new IsolateListener._(suite)._listen(sendPort);
   }
 
   /// Sends a message over [sendPort] indicating that the tests failed to load.