Make StreamController be a StreamSink, not just an EventSink.

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';
 
-testMultiController() {
+void testMultiController() {
   // Test normal flow.
   var c = new StreamController(sync: true);
   Events expectedEvents = new Events()
       ..add(42)
       ..add("dibs")
       ..error("error!")
       ..error("error too!")
       ..close();
   Events actualEvents = new Events.capture(c.stream.asBroadcastStream());
   expectedEvents.replay(c);
@@ skipping 378 matching lines @@
   sentEvents = new Events()
       ..add(5)..add(6)..add(4)..add(6)..add(8)..add(3)..add(4)..add(1)..close();
   expectedEvents = new Events()
       ..add(5)..add(4)..add(3)..add(1)..close();
   // Use 'distinct' as a filter with access to the previously emitted event.
   actualEvents = new Events.capture(c.stream.distinct((a, b) => a < b));
   sentEvents.replay(c);
   Expect.listEquals(expectedEvents.events, actualEvents.events);
 }
 
-testClosed() {
+void testClosed() {
   StreamController c = new StreamController(sync: true);
   Expect.isFalse(c.isClosed);
   c.add(42);
   Expect.isFalse(c.isClosed);
   c.addError("bad");
   Expect.isFalse(c.isClosed);
   c.close();
   Expect.isTrue(c.isClosed);
 }
 
 main() {
   testMultiController();
   testSingleController();
   testExtraMethods();
   testClosed();
 }