Native context: do not put public symbols and flags on the js builtins object.

src/json.js

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
 // -------------------------------------------------------------------
 // Imports
 
 var GlobalJSON = global.JSON;
 var InternalArray = utils.InternalArray;
 var MathMax;
 var MathMin;
 var ObjectHasOwnProperty;
 var ToNumber;
 var ToString;
+var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
 
 utils.Import(function(from) {
   MathMax = from.MathMax;
   MathMin = from.MathMin;
   ObjectHasOwnProperty = from.ObjectHasOwnProperty;
   ToNumber = from.ToNumber;
   ToString = from.ToString;
 });
 
 // -------------------------------------------------------------------
@@ skipping 196 matching lines @@
       gap = space;
     }
   } else {
     gap = "";
   }
   return JSONSerialize('', {'': value}, replacer, new InternalArray(), "", gap);
 }
 
 // -------------------------------------------------------------------
 
-%AddNamedProperty(GlobalJSON, symbolToStringTag, "JSON", READ_ONLY | DONT_ENUM);
+%AddNamedProperty(GlobalJSON, toStringTagSymbol, "JSON", READ_ONLY | DONT_ENUM);
 
 // Set up non-enumerable properties of the JSON object.
 utils.InstallFunctions(GlobalJSON, DONT_ENUM, [
   "parse", JSONParse,
   "stringify", JSONStringify
 ]);
 
 // -------------------------------------------------------------------
 // JSON Builtins
 
 function JsonSerializeAdapter(key, object) {
   var holder = {};
   holder[key] = object;
   // No need to pass the actual holder since there is no replacer function.
   return JSONSerialize(key, holder, UNDEFINED, new InternalArray(), "", "");
 }
 
 %InstallToContext(["json_serialize_adapter", JsonSerializeAdapter]);
 
 })