Make convert library strong-mode compliant.

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 d3648e786f88176e17db496a0157d1534908a61d..12d623a00e2b75f4203de611dd848b86556ecc3c 100644
--- a/sdk/lib/io/data_transformer.dart
+++ b/sdk/lib/io/data_transformer.dart
@@ -147,7 +147,7 @@ class ZLibCodec extends Codec<List<int>, List<int>> {
   /**
    * Get a [ZLibEncoder] for encoding to `ZLib` compressed data.
    */
-  Converter<List<int>, List<int>> get encoder =>
+  ZLibEncoder get encoder =>
       new ZLibEncoder(gzip: false, level: level, windowBits: windowBits,
                       memLevel: memLevel, strategy: strategy,
                       dictionary: dictionary, raw: raw);
@@ -155,7 +155,7 @@ class ZLibCodec extends Codec<List<int>, List<int>> {
   /**
    * Get a [ZLibDecoder] for decoding `ZLib` compressed data.
    */
-  Converter<List<int>, List<int>> get decoder =>
+  ZLibDecoder get decoder =>
       new ZLibDecoder(windowBits: windowBits, dictionary: dictionary, raw: raw);
 }
 
@@ -259,7 +259,7 @@ class GZipCodec extends Codec<List<int>, List<int>> {
   /**
    * Get a [ZLibEncoder] for encoding to `GZip` compressed data.
    */
-  Converter<List<int>, List<int>> get encoder =>
+  ZLibEncoder get encoder =>
       new ZLibEncoder(gzip: true, level: level, windowBits: windowBits,
                       memLevel: memLevel, strategy: strategy,
                       dictionary: dictionary, raw: raw);
@@ -267,7 +267,7 @@ class GZipCodec extends Codec<List<int>, List<int>> {
   /**
    * Get a [ZLibDecoder] for decoding `GZip` compressed data.
    */
-  Converter<List<int>, List<int>> get decoder =>
+  ZLibDecoder get decoder =>
       new ZLibDecoder(windowBits: windowBits, dictionary: dictionary, raw: raw);
 }
 
@@ -275,7 +275,8 @@ class GZipCodec extends Codec<List<int>, List<int>> {
  * The [ZLibEncoder] encoder is used by [ZLibCodec] and [GZipCodec] to compress
  * data.
  */
-class ZLibEncoder extends Converter<List<int>, List<int>> {
+class ZLibEncoder extends
+    ChunkedConverter<List<int>, List<int>, List<int>, List<int>> {
   /**
    * When true, `GZip` frames will be added to the compressed data.
    */
@@ -378,7 +379,8 @@ class ZLibEncoder extends Converter<List<int>, List<int>> {
 /**
  * The [ZLibDecoder] is used by [ZLibCodec] and [GZipCodec] to decompress data.
  */
-class ZLibDecoder extends Converter<List<int>, List<int>> {
+class ZLibDecoder extends
+    ChunkedConverter<List<int>, List<int>, 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