Introduce class Sink<T>.

sdk/lib/async/stream.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.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Core Stream types
 // -------------------------------------------------------------------
 
@@ skipping 1218 matching lines @@
    * In case of a `done` event the future completes with the given
    * [futureValue].
    */
   Future asFuture([var futureValue]);
 }
 
 
 /**
  * An interface that abstracts creation or handling of [Stream] events.
  */
-abstract class EventSink<T> {
+abstract class EventSink<T> implements Sink<T> {
   /** Create a data event */
   void add(T event);
   /** Create an async error. */
   void addError(errorEvent, [StackTrace stackTrace]);
   /** Request a stream to close. */
   void close();
 }
 
 
 /** [Stream] wrapper that only exposes the [Stream] interface. */
@@ skipping 232 matching lines @@
 class _ControllerEventSinkWrapper<T> implements EventSink<T> {
   EventSink _sink;
   _ControllerEventSinkWrapper(this._sink);
 
   void add(T data) { _sink.add(data); }
   void addError(error, [StackTrace stackTrace]) {
     _sink.addError(error, stackTrace);
   }
   void close() { _sink.close(); }
 }