Fix some strong mode issues in the core libraries.

sdk/lib/convert/chunked_conversion.dart

Index: sdk/lib/convert/chunked_conversion.dart
diff --git a/sdk/lib/convert/chunked_conversion.dart b/sdk/lib/convert/chunked_conversion.dart
index 710bef75c01129f76f197b0222bd08db13ac0c9e..ff1294fced06ca2405d97c72f03c4165b76a7b5e 100644
--- a/sdk/lib/convert/chunked_conversion.dart
+++ b/sdk/lib/convert/chunked_conversion.dart
@@ -6,16 +6,6 @@ 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.