Make dart:convert strong mode clean.

tests/lib/convert/chunked_conversion1_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:convert';
 
 import 'package:expect/expect.dart';
 
 // This test implements a new special interface that can be used to
 // send data more efficiently between two converters.
@@ skipping 36 matching lines @@
 }
 
 class BoolAdapterSink extends MyChunkedBoolSink {
   final _sink;
   BoolAdapterSink(this._sink);
   add(o) => _sink.add(o);
   close() => _sink.close();
   specialB(o) => add(o);
 }
 
-class IntBoolConverter1 extends
-    ChunkedConverter<List<int>, List<bool>, int, bool> {
+class IntBoolConverter1 extends Converter<List<int>, List<bool>> {
   List<bool> convert(List<int> input) => input.map((x) => x > 0).toList();
 
   startChunkedConversion(sink) {
     if (sink is! MyChunkedBoolSink) sink = new MyChunkedBoolSink.from(sink);
     return new IntBoolConverter1Sink(sink);
   }
 }
 
-class BoolIntConverter1 extends
-    ChunkedConverter<List<bool>, List<int>, bool, int> {
+class BoolIntConverter1 extends Converter<List<bool>, List<int>> {
   List<int> convert(List<bool> input) => input.map((x) => x ? 1 : 0).toList();
 
   startChunkedConversion(sink) {
     if (sink is! MyChunkedIntSink) sink = new MyChunkedIntSink.from(sink);
     return new BoolIntConverter1Sink(sink);
   }
 }
 
 int specialICounter = 0;
 int specialBCounter = 0;
@@ skipping 20 matching lines @@
     outSink.specialI(b ? 1 : 0);
   }
 
   specialB(bool b) {
     specialBCounter++;
     add(b);
   }
   close() => outSink.close();
 }
 
-class IdentityConverter extends ChunkedConverter {
+class IdentityConverter extends Converter {
   convert(x) => x;
 
   startChunkedConversion(sink) {
     return new IdentitySink(sink);
   }
 }
 
 class IdentitySink extends ChunkedConversionSink {
   final _sink;
   IdentitySink(this._sink);
@@ skipping 127 matching lines @@
   intSink.add(-3);
   intSink.add(3);
   intSink.close();
   Expect.isTrue(hasExecuted);
   Expect.equals(0, specialBCounter);
   specialBCounter = 0;
   Expect.equals(1, specialICounter);
   specialICounter = 0;
   hasExecuted = false;
 }