Treat Object and dynamic similarly

lib/runtime/dart/convert.js

 var convert;
 (function(exports) {
   'use strict';
   let ASCII = new AsciiCodec();
   let _ASCII_MASK = 127;
   let _allowInvalid = Symbol('_allowInvalid');
   let Codec$ = dart.generic(function(S, T) {
     class Codec extends core.Object {
       Codec() {
       }
@@ skipping 799 matching lines @@
       this[_reviver] = reviver;
       super.Converter();
     }
     convert(input) {
       return _parseJson(input, this[_reviver]);
     }
     startChunkedConversion(sink) {
       return new _JsonDecoderSink(this[_reviver], sink);
     }
     bind(stream) {
-      return dart.as(super.bind(stream), async.Stream$(core.Object));
+      return super.bind(stream);
     }
   }
   // Function _parseJson: (String, (dynamic, dynamic) → dynamic) → dynamic
   function _parseJson(source, reviver) {
     if (!(typeof source == string))
       throw new core.ArgumentError(source);
     let parsed = null;
     try {
       parsed = JSON.parse(source);
     } catch (e) {
@@ skipping 1490 matching lines @@
   exports.LineSplitter = LineSplitter;
   exports.StringConversionSink = StringConversionSink;
   exports.ClosableStringSink = ClosableStringSink;
   exports.UNICODE_REPLACEMENT_CHARACTER_RUNE = UNICODE_REPLACEMENT_CHARACTER_RUNE;
   exports.UNICODE_BOM_CHARACTER_RUNE = UNICODE_BOM_CHARACTER_RUNE;
   exports.UTF8 = UTF8;
   exports.Utf8Codec = Utf8Codec;
   exports.Utf8Encoder = Utf8Encoder;
   exports.Utf8Decoder = Utf8Decoder;
 })(convert || (convert = {}));