Make dart:convert strong mode clean.

sdk/lib/convert/utf.dart

Index: sdk/lib/convert/utf.dart
diff --git a/sdk/lib/convert/utf.dart b/sdk/lib/convert/utf.dart
index a93c9aec2c19a56680936d50c899900faed50a06..69bb72cb0f93ffac3b935a1523b6d1126a087ef1 100644
--- a/sdk/lib/convert/utf.dart
+++ b/sdk/lib/convert/utf.dart
@@ -76,8 +76,7 @@ class Utf8Codec extends Encoding {
  * This class converts strings to their UTF-8 code units (a list of
  * unsigned 8-bit integers).
  */
-class Utf8Encoder extends
-    ChunkedConverter<String, List<int>, String, List<int>> {
+class Utf8Encoder extends Converter<String, List<int>> {
 
   const Utf8Encoder();
 
@@ -305,8 +304,7 @@ class _Utf8EncoderSink extends _Utf8Encoder with StringConversionSinkMixin {
  * This class converts UTF-8 code units (lists of unsigned 8-bit integers)
  * to a string.
  */
-class Utf8Decoder extends
-    ChunkedConverter<List<int>, String, List<int>, String> {
+class Utf8Decoder extends Converter<List<int>, String> {
   final bool _allowMalformed;
 
   /**
@@ -369,7 +367,8 @@ class Utf8Decoder extends
   // Override the base-classes bind, to provide a better type.
   Stream<String> bind(Stream<List<int>> stream) => super.bind(stream);
 
-  external Converter<List<int>,dynamic> fuse(Converter<String, dynamic> next);
+  external Converter<List<int>, dynamic/*=T*/> fuse/*<T>*/(
+      Converter<String, dynamic/*=T*/> next);
 
   external static String _convertIntercepted(
       bool allowMalformed, List<int> codeUnits, int start, int end);