Update deprecations.

lib/src/base64/encoder_sink.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:convert';
 
 import 'encoder.dart';
 
-/// A [ChunkedConversionSink] for encoding chunks of data to Base64.
+/// This is deprecated.
+///
+/// Use the `Base64Encoder` class in `dart:convert` instead.
+@Deprecated("Will be removed in crypto 1.0.0.")
 class Base64EncoderSink extends ChunkedConversionSink<List<int>> {
   /// The encoder used to encode each chunk.
   final Base64Encoder _encoder;
 
   /// The underlying sink to which to emit the encoded strings.
   final ChunkedConversionSink<String> _outSink;
 
   /// The buffer of as-yet-unconverted bytes.
   ///
   /// This is used to ensure that we don't generate interstitial padding
@@ skipping 25 matching lines @@
   }
 
   void close() {
     if (_bufferCount > 0) {
       _outSink.add(_encoder.convert(_buffer.sublist(0, _bufferCount)));
     }
     _outSink.close();
   }
 }