Revert "Remove Sink and move CollectionSink to async."

sdk/lib/async/collection_sink.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.
-
-part of dart.async;
-
-typedef void _CollectionSinkCallback<T>(Collection<T> collection);
-typedef void _CollectionSinkErrorCallback(AsyncError error);
-
-/** Sink that stores incoming data in a collection. */
-class CollectionSink<T> implements StreamSink<T> {
-  final Collection<T> collection;
-  final _CollectionSinkCallback<T> _callback;
-  final _CollectionSinkErrorCallback _errorCallback;
-  bool _isClosed = false;
-
-  /**
-   * Create a sink that stores incoming values in a collection.
-   *
-   * The [collection] is the collection to add the values to.
-   *
-   * If [callback] is provided, then it's called with the collection as arugment
-   * when the sink's [close] method is called.
-   */
-  CollectionSink(this.collection,
-                { void onClose(Collection<T> collection),
-                  void onError(AsyncError error) })
-      : this._callback = onClose,
-        this._errorCallback = onError;
-
-  add(T value) {
-    if (_isClosed) throw new StateError("Adding to closed sink");
-    collection.add(value);
-  }
-
-  void signalError(AsyncError error) {
-    if (_isClosed) throw new StateError("Singalling error on closed sink");
-    if (_errorCallback != null) _errorCallback(error);
-  }
-
-  void close() {
-    if (_isClosed) throw new StateError("Closing closed sink");
-    _isClosed = true;
-    if (_callback != null) _callback(collection);
-  }
-}