Revert "The expected key is a valid identifier, which is already free of \\, <0x20, "."

test/mjsunit/json2.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 165 matching lines @@
 non_enum.a = 1;
 Object.defineProperty(non_enum, "b", { value: 2, enumerable: false });
 non_enum.c = 3;
 TestStringify('{"a":1,"c":3}', non_enum);
 
 var str = "external";
 try {
   externalizeString(str, true);
 } catch (e) { }
 TestStringify("\"external\"", str, null, 0);
+
+var o = {};
+o.somespecialproperty = 10;
+o["\x19"] = 10;
+assertThrows("JSON.parse('{\"somespecialproperty\":100, \"\x19\":10}')");