Remove Sink and move CollectionSink to async.

tests/lib/async/event_helper.dart

 // Copyright (c) 2012, 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 event_helper;
 
 import 'dart:async';
 
 abstract class Event {
   void replay(StreamSink sink);
@@ skipping 54 matching lines @@
   Events();
   Events.fromIterable(Iterable iterable) {
     for (var value in iterable) add(value);
     close();
   }
 
   /** Capture events from a stream into a new [Events] object. */
   factory Events.capture(Stream stream,
                          { bool unsubscribeOnError: false }) = CaptureEvents;
 
-  // Sink interface.
+  // StreamSink interface.
   add(var value) { events.add(new DataEvent(value)); }
 
   void signalError(AsyncError error) {
     events.add(new ErrorEvent(error));
   }
 
   void close() {
     events.add(const DoneEvent());
   }
 
@@ skipping 73 matching lines @@
   }
 
   void resume() {
     subscription.resume();
   }
 
   void onDone(void action()) {
     onDoneSignal.future.whenComplete(action);
   }
 }