Pass actual TestPlatform and OperatingSystem values to Suite.

lib/src/runner/browser/browser_manager.dart

Index: lib/src/runner/browser/browser_manager.dart
diff --git a/lib/src/runner/browser/browser_manager.dart b/lib/src/runner/browser/browser_manager.dart
index 0442d82bd35819400cdce2c802d588f962c6142b..76f76e64e82570f70e903be1f8023aa09f474b7c 100644
--- a/lib/src/runner/browser/browser_manager.dart
+++ b/lib/src/runner/browser/browser_manager.dart
@@ -139,6 +139,7 @@ class BrowserManager {
       var testChannel = suiteChannel.virtualChannel(test['channel']);
       return new IframeTest(test['name'], testMetadata, testChannel,
           mapper: mapper);
-    }), metadata: metadata, path: path, onClose: () => closeIframe());
+    }), platform: browser, metadata: metadata, path: path,
+        onClose: () => closeIframe());
   }
 }