don't run dart gen on JS patch code

test/dart_codegen/expect/convert/json.dart

 part of dart.convert;
 
 class JsonUnsupportedObjectError extends Error {
   final unsupportedObject;
   final cause;
   JsonUnsupportedObjectError(this.unsupportedObject, {this.cause});
   String toString() {
     if (cause != null) {
       return "Converting object to an encodable object failed.";
     } else {
@@ skipping 188 matching lines @@
     if (!_isDone) {
       _isDone = true;
       _sink.close();
     }
   }
 }
 class JsonDecoder extends Converter<String, Object> {
   final _Reviver _reviver;
   const JsonDecoder([reviver(var key, var value)]) : this._reviver = reviver;
   dynamic convert(String input) => _parseJson(input, _reviver);
-  StringConversionSink startChunkedConversion(Sink<Object> sink) {
-    return new _JsonDecoderSink(_reviver, sink);
-  }
+  external StringConversionSink startChunkedConversion(Sink<Object> sink);
   Stream<Object> bind(Stream<String> stream) => ((__x14) => DDC$RT.cast(__x14,
       DDC$RT.type((DDC$async$.Stream<dynamic> _) {}),
       DDC$RT.type((DDC$async$.Stream<Object> _) {}), "CastDynamic",
-      """line 509, column 49 of dart:convert/json.dart: """,
+      """line 507, column 49 of dart:convert/json.dart: """,
       __x14 is DDC$async$.Stream<Object>, false))(super.bind(stream));
 }
-_parseJson(String source, reviver(key, value)) {
-  if (source is! String) throw new ArgumentError(source);
-  var parsed;
-  try {
-    parsed = JS('=Object|JSExtendableArray|Null|bool|num|String',
-        'JSON.parse(#)', source);
-  } catch (e) {
-    throw new FormatException(JS('String', 'String(#)', e));
-  }
-  if (reviver == null) {
-    return _convertJsonToDartLazy(parsed);
-  } else {
-    return _convertJsonToDart(parsed, reviver);
-  }
-}
+external _parseJson(String source, reviver(key, value));
 Object _defaultToEncodable(object) => object.toJson();
 abstract class _JsonStringifier {
   static const int BACKSPACE = 0x08;
   static const int TAB = 0x09;
   static const int NEWLINE = 0x0a;
   static const int CARRIAGE_RETURN = 0x0d;
   static const int FORM_FEED = 0x0c;
   static const int QUOTE = 0x22;
   static const int CHAR_0 = 0x30;
   static const int BACKSLASH = 0x5c;
@@ skipping 84 matching lines @@
       }
       _removeSeen(object);
     } catch (e) {
       throw new JsonUnsupportedObjectError(object, cause: e);
     }
   }
   bool writeJsonValue(object) {
     if (object is num) {
       if (!object.isFinite) return false;
       writeNumber(DDC$RT.cast(object, dynamic, num, "CastGeneral",
-          """line 692, column 19 of dart:convert/json.dart: """, object is num,
+          """line 673, column 19 of dart:convert/json.dart: """, object is num,
           true));
       return true;
     } else if (identical(object, true)) {
       writeString('true');
       return true;
     } else if (identical(object, false)) {
       writeString('false');
       return true;
     } else if (object == null) {
       writeString('null');
       return true;
     } else if (object is String) {
       writeString('"');
       writeStringContent(DDC$RT.cast(object, dynamic, String, "CastGeneral",
-          """line 705, column 26 of dart:convert/json.dart: """,
+          """line 686, column 26 of dart:convert/json.dart: """,
           object is String, true));
       writeString('"');
       return true;
     } else if (object is List) {
       _checkCycle(object);
       writeList(DDC$RT.cast(object, dynamic, DDC$RT.type((List<dynamic> _) {}),
-          "CastGeneral", """line 710, column 17 of dart:convert/json.dart: """,
+          "CastGeneral", """line 691, column 17 of dart:convert/json.dart: """,
           object is List<dynamic>, true));
       _removeSeen(object);
       return true;
     } else if (object is Map) {
       _checkCycle(object);
       writeMap(DDC$RT.cast(object, dynamic,
           DDC$RT.type((Map<String, Object> _) {}), "CastGeneral",
-          """line 715, column 16 of dart:convert/json.dart: """,
+          """line 696, column 16 of dart:convert/json.dart: """,
           object is Map<String, Object>, false));
       _removeSeen(object);
       return true;
     } else {
       return false;
     }
   }
   void writeList(List list) {
     writeString('[');
     if (list.length > 0) {
@@ skipping 43 matching lines @@
   void writeMap(Map map) {
     if (map.isEmpty) {
       writeString('{}');
     } else {
       writeString('{\n');
       _indentLevel++;
       bool first = true;
       map.forEach(((__x23) => DDC$RT.wrap(
           (dynamic f(String __u15, Object __u16)) {
         dynamic c(String x0, Object x1) => f(DDC$RT.cast(x0, dynamic, String,
-            "CastParam", """line 792, column 19 of dart:convert/json.dart: """,
+            "CastParam", """line 773, column 19 of dart:convert/json.dart: """,
             x0 is String, true), x1);
         return f == null ? null : c;
       }, __x23, __t20, __t17, "WrapLiteral",
-          """line 792, column 19 of dart:convert/json.dart: """,
+          """line 773, column 19 of dart:convert/json.dart: """,
           __x23 is __t17))((String key, Object value) {
         if (!first) {
           writeString(",\n");
         }
         writeIndentation(_indentLevel);
         writeString('"');
         writeStringContent(key);
         writeString('": ');
         writeObject(value);
         first = false;
       }));
       writeString('\n');
       _indentLevel--;
       writeIndentation(_indentLevel);
       writeString('}');
     }
   }
 }
 class _JsonStringStringifier extends _JsonStringifier {
   final StringSink _sink;
   _JsonStringStringifier(this._sink, _toEncodable) : super(DDC$RT.cast(
           _toEncodable, dynamic, __t24, "CastGeneral",
-          """line 817, column 60 of dart:convert/json.dart: """,
+          """line 798, column 60 of dart:convert/json.dart: """,
           _toEncodable is __t24, false));
   static String stringify(object, toEncodable(object), String indent) {
     StringBuffer output = new StringBuffer();
     printOn(object, output, toEncodable, indent);
     return output.toString();
   }
   static void printOn(
       object, StringSink output, toEncodable(object), String indent) {
     var stringifier;
     if (indent == null) {
@@ skipping 27 matching lines @@
     for (int i = 0; i < count; i++) writeString(_indent);
   }
 }
 class _JsonUtf8Stringifier extends _JsonStringifier {
   final int bufferSize;
   final Function addChunk;
   Uint8List buffer;
   int index = 0;
   _JsonUtf8Stringifier(toEncodable, int bufferSize, this.addChunk)
       : super(DDC$RT.cast(toEncodable, dynamic, __t24, "CastGeneral",
-          """line 893, column 15 of dart:convert/json.dart: """,
+          """line 874, column 15 of dart:convert/json.dart: """,
           toEncodable is __t24, false)),
         this.bufferSize = bufferSize,
         buffer = new Uint8List(bufferSize);
   static void stringify(Object object, List<int> indent,
       toEncodableFunction(Object o), int bufferSize,
       void addChunk(Uint8List chunk, int start, int end)) {
     _JsonUtf8Stringifier stringifier;
     if (indent != null) {
       stringifier = new _JsonUtf8StringifierPretty(
           toEncodableFunction, indent, bufferSize, addChunk);
@@ skipping 80 matching lines @@
     }
     buffer[index++] = byte;
   }
 }
 class _JsonUtf8StringifierPretty extends _JsonUtf8Stringifier
     with _JsonPrettyPrintMixin {
   final List<int> indent;
   _JsonUtf8StringifierPretty(
       toEncodableFunction, this.indent, bufferSize, addChunk)
       : super(toEncodableFunction, DDC$RT.cast(bufferSize, dynamic, int,
-          "CastGeneral", """line 1031, column 36 of dart:convert/json.dart: """,
+          "CastGeneral", """line 1012, column 36 of dart:convert/json.dart: """,
           bufferSize is int, true), DDC$RT.cast(addChunk, dynamic, Function,
-          "CastGeneral", """line 1031, column 48 of dart:convert/json.dart: """,
+          "CastGeneral", """line 1012, column 48 of dart:convert/json.dart: """,
           addChunk is Function, true));
   void writeIndentation(int count) {
     List<int> indent = this.indent;
     int indentLength = indent.length;
     if (indentLength == 1) {
       int char = indent[0];
       while (count > 0) {
         writeByte(char);
         count -= 1;
       }
@@ skipping 11 matching lines @@
         }
       }
     }
   }
 }
 typedef dynamic __t7(dynamic __u8);
 typedef dynamic __t11(Object __u12);
 typedef void __t17(dynamic __u18, dynamic __u19);
 typedef dynamic __t20(String __u21, Object __u22);
 typedef Object __t24(Object __u25);