Refactor groups to pipe them through to the runner.

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 034164563d73d55a22146a6de6bb71cb9ab3e6ab..875672ed6863dacef93ca8082a3568f4f373c5d0 100644
--- a/lib/src/runner/browser/iframe_test.dart
+++ b/lib/src/runner/browser/iframe_test.dart
@@ -7,15 +7,17 @@ library test.runner.browser.iframe_test;
 import '../../backend/live_test.dart';
 import '../../backend/live_test_controller.dart';
 import '../../backend/metadata.dart';
+import '../../backend/operating_system.dart';
 import '../../backend/state.dart';
 import '../../backend/suite.dart';
 import '../../backend/test.dart';
+import '../../backend/test_platform.dart';
 import '../../util/multi_channel.dart';
 import '../../util/remote_exception.dart';
 import '../../util/stack_trace_mapper.dart';
 
 /// A test in a running iframe.
-class IframeTest implements Test {
+class IframeTest extends Test {
   final String name;
   final Metadata metadata;
 
@@ -71,10 +73,10 @@ class IframeTest implements Test {
     return controller.liveTest;
   }
 
-  Test change({String name, Metadata metadata}) {
-    if (name == name && metadata == this.metadata) return this;
-    if (name == null) name = this.name;
-    if (metadata == null) metadata = this.metadata;
-    return new IframeTest(name, metadata, _channel);
+  Test forPlatform(TestPlatform platform, {OperatingSystem os}) {
+    if (!metadata.testOn.evaluate(platform, os: os)) return null;
+    return new IframeTest(
+        name, metadata.forPlatform(platform, os: os), _channel,
+        mapper: _mapper);
   }
 }