Make dart:convert strong mode clean.

sdk/lib/io/data_transformer.dart

Index: sdk/lib/io/data_transformer.dart
diff --git a/sdk/lib/io/data_transformer.dart b/sdk/lib/io/data_transformer.dart
index 12d623a00e2b75f4203de611dd848b86556ecc3c..968fd20ebcbb8d2c83f99666e4dc434b7046cf8f 100644
--- a/sdk/lib/io/data_transformer.dart
+++ b/sdk/lib/io/data_transformer.dart
@@ -275,8 +275,7 @@ class GZipCodec extends Codec<List<int>, List<int>> {
  * The [ZLibEncoder] encoder is used by [ZLibCodec] and [GZipCodec] to compress
  * data.
  */
-class ZLibEncoder extends
-    ChunkedConverter<List<int>, List<int>, List<int>, List<int>> {
+class ZLibEncoder extends Converter<List<int>, List<int>> {
   /**
    * When true, `GZip` frames will be added to the compressed data.
    */
@@ -379,8 +378,7 @@ class ZLibEncoder extends
 /**
  * The [ZLibDecoder] is used by [ZLibCodec] and [GZipCodec] to decompress data.
  */
-class ZLibDecoder extends
-    ChunkedConverter<List<int>, List<int>, List<int>, List<int>> {
+class ZLibDecoder extends  Converter<List<int>, List<int>> {
   /**
    * Base two logarithm of the window size (the size of the history buffer). It
    * should be in the range `8..15`. Larger values result in better compression