Make asBroadcastStream take two callbacks.

tests/lib/async/stream_controller_test.dart

 // Copyright (c) 2011, 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.
 
 // Test the basic StreamController and StreamController.singleSubscription.
 library stream_controller_test;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'event_helper.dart';
@@ skipping 88 matching lines @@
   // Test transform.
   c = new StreamController(sync: true);
   sentEvents = new Events()..add("a")..error(42)..add("b")..close();
   expectedEvents =
       new Events()..error("a")..add(42)..error("b")..add("foo")..close();
   actualEvents = new Events.capture(c.stream.asBroadcastStream().transform(
       new StreamTransformer(
           handleData: (v, s) { s.addError(v); },
           handleError: (e, s) { s.add(e); },
           handleDone: (s) {
-
             s.add("foo");
-
             s.close();
-
           })));
   sentEvents.replay(c);
   Expect.listEquals(expectedEvents.events, actualEvents.events);
 
   // Test multiple filters.
   c = new StreamController(sync: true);
   sentEvents = new Events()..add(42)
                            ..add("snugglefluffy")
                            ..add(7)
                            ..add("42")
@@ skipping 294 matching lines @@
   c.close();
   Expect.isTrue(c.isClosed);
 }
 
 main() {
   testMultiController();
   testSingleController();
   testExtraMethods();
   testClosed();
 }