[json] handle proxies in BasicJsonSerializer.

src/js/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();
 
@@ skipping 183 matching lines @@
     } else {
       return SerializeObject(value, replacer, stack, indent, gap);
     }
   }
   // Undefined or a callable object.
   return UNDEFINED;
 }
 
 
 function JSONStringify(value, replacer, space) {
-  if (arguments.length === 1 && !IS_PROXY(value)) {
-    return %BasicJSONStringify(value, "");
-  }
+  if (arguments.length === 1) return %BasicJSONStringify(value, "");
   if (!IS_CALLABLE(replacer) && %is_arraylike(replacer)) {
     var property_list = new InternalArray();
     var seen_properties = new GlobalSet();
     var length = TO_LENGTH(replacer.length);
     for (var i = 0; i < length; i++) {
       var v = replacer[i];
       var item;
       if (IS_STRING(v)) {
         item = v;
       } else if (IS_NUMBER(v)) {
@@ skipping 24 matching lines @@
     gap = %_SubString("          ", 0, space);
   } else if (IS_STRING(space)) {
     if (space.length > 10) {
       gap = %_SubString(space, 0, 10);
     } else {
       gap = space;
     }
   } else {
     gap = "";
   }
-  if (!IS_CALLABLE(replacer) && !property_list && !IS_PROXY(value)) {
+  if (!IS_CALLABLE(replacer) && !property_list) {
     return %BasicJSONStringify(value, gap);
   }
   return JSONSerialize('', {'': value}, replacer, new Stack(), "", gap);
 }
 
 // -------------------------------------------------------------------
 
 %AddNamedProperty(GlobalJSON, toStringTagSymbol, "JSON", READ_ONLY | DONT_ENUM);
 
 // Set up non-enumerable properties of the JSON object.
@@ skipping 29 matching lines @@
   // No need to pass the actual holder since there is no replacer function.
   var current_indent = "";
   for (var i = 0; i < indent; i++) current_indent += gap;
   return JSONSerialize(
       key, holder, UNDEFINED, new Stack(), current_indent, gap);
 }
 
 %InstallToContext(["json_serialize_adapter", JsonSerializeAdapter]);
 
 })