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

lib/src/runner/browser/iframe_test.dart

Index: lib/src/runner/browser/iframe_test.dart
diff --git a/lib/src/runner/browser/iframe_test.dart b/lib/src/runner/browser/iframe_test.dart
index 6b799419c5ba8458639c86dae4c79d83180fee85..bb54e786f6f0ea3ef7d30beff163b494b50babf3 100644
--- a/lib/src/runner/browser/iframe_test.dart
+++ b/lib/src/runner/browser/iframe_test.dart
@@ -60,4 +60,10 @@ class IframeTest implements Test {
     });
     return controller.liveTest;
   }
+
+  Test change({String name, Metadata metadata}) {
+    if (name == null) name = this.name;
+    if (metadata == null) metadata = this.metadata;
+    return new IframeTest(name, metadata, _channel);
+  }
 }