fix dummy setters -- grammar requires an identifier

test/codegen/expect/convert/convert.js

 var convert;
 (function(exports) {
   'use strict';
   // Function _convertJsonToDart: (dynamic, (dynamic, dynamic) → dynamic) → dynamic
   function _convertJsonToDart(json, reviver) {
     dart.assert(reviver !== null);
     // Function walk: (dynamic) → dynamic
     function walk(e) {
       if (dart.notNull(e == null) || dart.notNull(typeof e != "object")) {
         return e;
@@ skipping 685 matching lines @@
       if (name === null)
         return null;
       name = name.toLowerCase();
       return _nameToEncoding.get(name);
     }
   }
   dart.defineLazyProperties(Encoding, {
     get _nameToEncoding() {
       return dart.map({"iso_8859-1:1987": LATIN1, "iso-ir-100": LATIN1, "iso_8859-1": LATIN1, "iso-8859-1": LATIN1, latin1: LATIN1, l1: LATIN1, ibm819: LATIN1, cp819: LATIN1, csisolatin1: LATIN1, "iso-ir-6": ASCII, "ansi_x3.4-1968": ASCII, "ansi_x3.4-1986": ASCII, "iso_646.irv:1991": ASCII, "iso646-us": ASCII, "us-ascii": ASCII, us: ASCII, ibm367: ASCII, cp367: ASCII, csascii: ASCII, ascii: ASCII, csutf8: UTF8, "utf-8": UTF8});
     },
-    set _nameToEncoding() {}
+    set _nameToEncoding(_) {}
   });
   let HTML_ESCAPE = new HtmlEscape();
   class HtmlEscapeMode extends dart.Object {
     HtmlEscapeMode$_(_name, escapeLtGt, escapeQuot, escapeApos, escapeSlash) {
       this._name = _name;
       this.escapeLtGt = escapeLtGt;
       this.escapeQuot = escapeQuot;
       this.escapeApos = escapeApos;
       this.escapeSlash = escapeSlash;
     }
@@ skipping 1544 matching lines @@
   exports.ClosableStringSink = ClosableStringSink;
   exports.StringConversionSinkBase = StringConversionSinkBase;
   exports.StringConversionSinkMixin = StringConversionSinkMixin;
   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 = {}));