Add BrowserManager and IframeTest for communicating with browser tests.

lib/src/utils.dart

 // Copyright (c) 2013, 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 unittest.utils;
 
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 45 matching lines @@
       if (element is Iterable) {
         helper(element);
       } else {
         result.add(element);
       }
     }
   }
   helper(nested);
   return result;
 }
+
+/// Returns a sink that maps events sent to [original] using [fn].
+StreamSink mapSink(StreamSink original, fn(event)) {
+  var controller = new StreamController(sync: true);
+  controller.stream.listen(
+      (event) => original.add(fn(event)),
+      onError: (error, stackTrace) => original.addError(error, stackTrace),
+      onDone: () => original.close());
+  return controller.sink;
+}