Avoid runtime type errors in checked mode for ChunkedConverters.

sdk/lib/convert/utf.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.convert;
 
 /** The Unicode Replacement character `U+FFFD` (�). */
 const int UNICODE_REPLACEMENT_CHARACTER_RUNE = 0xFFFD;
 
 /** The Unicode Byte Order Marker (BOM) character `U+FEFF`. */
@@ skipping 58 matching lines @@
   Utf8Encoder get encoder => const Utf8Encoder();
   Utf8Decoder get decoder {
     return new Utf8Decoder(allowMalformed: _allowMalformed);
   }
 }
 
 /**
  * This class converts strings to their UTF-8 code units (a list of
  * unsigned 8-bit integers).
  */
-class Utf8Encoder extends Converter<String, List<int>> {
+class Utf8Encoder extends Converter<String, List<int>>
+    implements ChunkedConverter<String, List<int>, String, List<int>> {
 
   const Utf8Encoder();
 
   /**
    * Converts [string] to its UTF-8 code units (a list of
    * unsigned 8-bit integers).
    *
    * If [start] and [end] are provided, only the substring
    * `string.substring(start, end)` is converted.
    */
@@ skipping 207 matching lines @@
   }
 
   // TODO(floitsch): implement asUtf8Sink. Sligthly complicated because it
   // needs to deal with malformed input.
 }
 
 /**
  * This class converts UTF-8 code units (lists of unsigned 8-bit integers)
  * to a string.
  */
-class Utf8Decoder extends Converter<List<int>, String> {
+class Utf8Decoder extends Converter<List<int>, String>
+    implements ChunkedConverter<List<int>, String, List<int>, String> {
+
   final bool _allowMalformed;
 
   /**
    * Instantiates a new [Utf8Decoder].
    *
    * The optional [allowMalformed] argument defines how [convert] deals
    * with invalid or unterminated character sequences.
    *
    * If it is `true` [convert] replaces invalid (or unterminated) character
    * sequences with the Unicode Replacement character `U+FFFD` (�). Otherwise
@@ skipping 245 matching lines @@
       }
       break loop;
     }
     if (expectedUnits > 0) {
       _value = value;
       _expectedUnits = expectedUnits;
       _extraUnits = extraUnits;
     }
   }
 }