Make StreamController be a StreamSink, not just an EventSink.

tests/lib/async/stream_controller_test.dart

Index: tests/lib/async/stream_controller_test.dart
diff --git a/tests/lib/async/stream_controller_test.dart b/tests/lib/async/stream_controller_test.dart
index 006d83ae43dbdbd8d239ba240ebf6aaa72a65d32..3f2a48b1a18041ab5fd5b8fdf2224fc4d36379d3 100644
--- a/tests/lib/async/stream_controller_test.dart
+++ b/tests/lib/async/stream_controller_test.dart
@@ -9,7 +9,7 @@ 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()
@@ -405,7 +405,7 @@ testExtraMethods() {
   Expect.listEquals(expectedEvents.events, actualEvents.events);
 }
 
-testClosed() {
+void testClosed() {
   StreamController c = new StreamController(sync: true);
   Expect.isFalse(c.isClosed);
   c.add(42);