Fix some strong mode issues in the core libraries.

sdk/lib/convert/chunked_conversion.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.convert;
 
 typedef void _ChunkedConversionCallback<T>(T accumulated);
 
-/// This class is deprecated. Extend [Converter] directly.
-@deprecated
-abstract class ChunkedConverter<S, T, S2, T2> extends Converter<S, T> {
-  const ChunkedConverter() : super();
-
-  dynamic bind(dynamic other) => super.bind(other);
-  dynamic startChunkedConversion(dynamic sink) =>
-      super.startChunkedConversion(sink);
-}
-
 /**
  * A [ChunkedConversionSink] is used to transmit data more efficiently between
  * two converters during chunked conversions.
  *
  * The basic `ChunkedConversionSink` is just a [Sink], and converters should
  * work with a plain `Sink`, but may work more efficiently with certain
  * specialized types of `ChunkedConversionSink`.
  *
  * It is recommended that implementations of `ChunkedConversionSink` extend
  * this class, to inherit any further methods that may be added to the class.
@@ skipping 68 matching lines @@
   }
 
   void addError(Object error, [StackTrace stackTrace]) {
     _eventSink.addError(error, stackTrace);
   }
 
   void close() {
     _chunkedSink.close();
   }
 }