Fix some strong mode issues in the core libraries.

sdk/lib/io/string_transformer.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.
 
 part of dart.io;
 
 /// The current system encoding.
 ///
 /// This us used for converting from bytes to/from String when
 /// communicating on stdin, stdout and stderr.
@@ skipping 24 matching lines @@
 
   Converter<List<int>, String> get decoder {
     if (Platform.operatingSystem == "windows") {
       return const _WindowsCodePageDecoder();
     } else {
       return const Utf8Decoder();
     }
   }
 }
 
-class _WindowsCodePageEncoder extends Converter<String, List<int>>
-    implements ChunkedConverter<String, List<int>, String, List<int>> {
+class _WindowsCodePageEncoder extends Converter<String, List<int>> {
   const _WindowsCodePageEncoder();
 
   List<int> convert(String input) {
     List<int> encoded = _encodeString(input);
     if (encoded == null) {
       throw new FormatException("Invalid character for encoding");
     }
     return encoded;
   }
 
@@ skipping 29 matching lines @@
 
   void addSlice(String source, int start, int end, bool isLast) {
     if (start != 0 || end != source.length) {
       source = source.substring(start, end);
     }
     add(source);
     if (isLast) close();
   }
 }
 
-class _WindowsCodePageDecoder extends Converter<List<int>, String>
-    implements ChunkedConverter<List<int>, String, List<int>, String> {
+class _WindowsCodePageDecoder extends Converter<List<int>, String> {
   const _WindowsCodePageDecoder();
 
   String convert(List<int> input) {
     return _decodeBytes(input);
   }
 
   /**
    * Starts a chunked conversion.
    */
   ByteConversionSink startChunkedConversion(Sink<String> sink) {
@@ skipping 12 matching lines @@
   _WindowsCodePageDecoderSink(this._sink);
 
   void close() {
     _sink.close();
   }
 
   void add(List<int> bytes) {
     _sink.add(_WindowsCodePageDecoder._decodeBytes(bytes));
   }
 }