Pass actual TestPlatform and OperatingSystem values to Suite.

lib/src/runner/browser/browser_manager.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.runner.browser.browser_manager;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:http_parser/http_parser.dart';
@@ skipping 121 matching lines @@
       await new Future.error(
           new LoadException(path, asyncError.error),
           asyncError.stackTrace);
     }
 
     return new Suite(response["tests"].map((test) {
       var testMetadata = new Metadata.deserialize(test['metadata']);
       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());
   }
 }