Avoid runtime type errors in checked mode for ChunkedConverters.

sdk/lib/convert/json.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;
 
 /**
  * Error thrown by JSON serialization if an object cannot be serialized.
  *
  * The [unsupportedObject] field holds that object that failed to be serialized.
@@ skipping 141 matching lines @@
 
   JsonDecoder get decoder {
     if (_reviver == null) return const JsonDecoder();
     return new JsonDecoder(_reviver);
   }
 }
 
 /**
  * This class converts JSON objects to strings.
  */
-class JsonEncoder extends Converter<Object, String> {
+class JsonEncoder extends Converter<Object, String>
+    implements ChunkedConverter<Object, String, Object, String> {
   /**
    * The string used for indention.
    *
    * When generating multi-line output, this string is inserted once at the
    * beginning of each indented line for each level of indentation.
    *
    * If `null`, the output is encoded as a single line.
    */
   final String indent;
 
@@ skipping 104 matching lines @@
   }
 }
 
 /**
  * Encoder that encodes a single object as a UTF-8 encoded JSON string.
  *
  * This encoder works equivalently to first converting the object to
  * a JSON string, and then UTF-8 encoding the string, but without
  * creating an intermediate string.
  */
-class JsonUtf8Encoder extends Converter<Object, List<int>> {
+class JsonUtf8Encoder extends Converter<Object, List<int>>
+    implements ChunkedConverter<Object, List<int>, Object, List<int>> {
+
   /** Default buffer size used by the JSON-to-UTF-8 encoder. */
   static const int DEFAULT_BUFFER_SIZE = 256;
   /** Indentation used in pretty-print mode, `null` if not pretty. */
   final List<int> _indent;
   /** Function called with each un-encodable object encountered. */
   final _ToEncodable _toEncodable;
   /** UTF-8 buffer size. */
   final int _bufferSize;
 
   /**
@@ skipping 165 matching lines @@
     if (!_isDone) {
       _isDone = true;
       _sink.close();
     }
   }
 }
 
 /**
  * This class parses JSON strings and builds the corresponding objects.
  */
-class JsonDecoder extends Converter<String, Object> {
+class JsonDecoder extends Converter<String, Object>
+    implements ChunkedConverter<String, Object, String, Object> {
   final _Reviver _reviver;
   /**
    * Constructs a new JsonDecoder.
    *
    * The [reviver] may be `null`.
    */
   const JsonDecoder([reviver(var key, var value)]) : this._reviver = reviver;
 
   /**
    * Converts the given JSON-string [input] to its corresponding object.
@@ skipping 571 matching lines @@
         buffer.setRange(index, end, indent);
         index = end;
       } else {
         for (int i = 0; i < indentLength; i++) {
           writeByte(indent[i]);
         }
       }
     }
   }
 }