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

lib/src/runner/loader.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.loader;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
@@ skipping 130 matching lines @@
       return new Future.sync(() {
         if (_pubServeUrl != null && !p.isWithin('test', path)) {
           throw new LoadException(path,
               'When using "pub serve", all test files must be in test/.');
         }
 
         if (platform == TestPlatform.vm) return _loadVmFile(path, metadata);
         assert(platform.isBrowser);
         return _loadBrowserFile(path, platform, metadata);
       }).then((suite) {
-        if (suite == null) return;
-
-        controller.add(suite.filter(platform, os: currentOS));
+        if (suite != null) controller.add(suite);
       }).catchError(controller.addError);
     }).then((_) => controller.close());
 
     return controller.stream;
   }
 
   /// Load the test suite at [path] in [platform].
   ///
   /// [metadata] is the suite-level metadata for the test.
   Future<Suite> _loadBrowserFile(String path, TestPlatform platform,
@@ skipping 75 matching lines @@
   Future close() {
     for (var isolate in _isolates) {
       isolate.kill();
     }
     _isolates.clear();
 
     if (_browserServerCompleter == null) return new Future.value();
     return _browserServer.then((browserServer) => browserServer.close());
   }
 }