Fix bad (too specialized) types.

sdk/lib/io/string_transformer.dart

Index: sdk/lib/io/string_transformer.dart
diff --git a/sdk/lib/io/string_transformer.dart b/sdk/lib/io/string_transformer.dart
index d4f13fc8337f4a3d4349c8064d4e7a8824db564f..91787573df72e6946106951e3e03a778dce7b902 100644
--- a/sdk/lib/io/string_transformer.dart
+++ b/sdk/lib/io/string_transformer.dart
@@ -63,7 +63,7 @@ class _WindowsCodePageEncoderSink extends StringConversionSinkBase {
   // TODO(floitsch): provide more efficient conversions when the input is
   // not a String.
 
-  final ByteConversionSink _sink;
+  final ChunkedConversionSink<List<int>> _sink;
 
   _WindowsCodePageEncoderSink(this._sink);
 
@@ -115,7 +115,7 @@ class _WindowsCodePageDecoderSink extends ByteConversionSinkBase {
   // TODO(floitsch): provide more efficient conversions when the input is
   // a slice.
 
-  final StringConversionSink _sink;
+  final ChunkedConversionSink<String> _sink;
 
   _WindowsCodePageDecoderSink(this._sink);