Make convert library strong-mode compliant.

runtime/lib/convert_patch.dart

 // Copyright (c) 2014, 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:_internal" show POWERS_OF_TEN;
 
 // JSON conversion.
 
 patch _parseJson(String json, reviver(var key, var value)) {
   _BuildJsonListener listener;
@@ skipping 21 matching lines @@
   }
 
   // Allow intercepting of UTF-8 decoding when built-in lists are passed.
   /* patch */
   static String _convertIntercepted(
       bool allowMalformed, List<int> codeUnits, int start, int end) {
     return null;  // This call was not intercepted.
   }
 }
 
-class _JsonUtf8Decoder extends Converter<List<int>, Object> {
+class _JsonUtf8Decoder extends
+    ChunkedConverter<List<int>, Object, List<int>, Object> {
   final _Reviver _reviver;
   final bool _allowMalformed;
 
   _JsonUtf8Decoder(this._reviver, this._allowMalformed);
 
-  dynamic convert(List<int> input) {
+  Object convert(List<int> input) {
     var parser = _JsonUtf8DecoderSink._createParser(_reviver, _allowMalformed);
     parser.chunk = input;
     parser.chunkEnd = input.length;
     parser.parse(0);
     return parser.result;
   }
 
   ByteConversionSink startChunkedConversion(Sink<Object> sink) {
     return new _JsonUtf8DecoderSink(_reviver, sink, _allowMalformed);
   }
@@ skipping 1706 matching lines @@
     _parser.parse(start);
   }
 
   void close() {
     _parser.close();
     var decoded = _parser.result;
     _sink.add(decoded);
     _sink.close();
   }
 }