[json] implement JSON.stringify gap pre-processing in C++.

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 215 matching lines @@
     replacer = property_list;
   }
   if (IS_OBJECT(space)) {
     // Unwrap 'space' if it is wrapped
     if (IS_NUMBER_WRAPPER(space)) {
       space = TO_NUMBER(space);
     } else if (IS_STRING_WRAPPER(space)) {
       space = TO_STRING(space);
     }
   }
+  if (!IS_CALLABLE(replacer) && !property_list) {
+    return %BasicJSONStringify(value, space);
+  }
   var gap;
   if (IS_NUMBER(space)) {
     space = MaxSimple(0, MinSimple(TO_INTEGER(space), 10));
     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) {
-    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.
 utils.InstallFunctions(GlobalJSON, DONT_ENUM, [
   "parse", JSONParse,
@@ skipping 12 matching lines @@
   }
   return o.toISOString();
 }
 
 // Set up non-enumerable functions of the Date prototype object.
 utils.InstallFunctions(GlobalDate.prototype, DONT_ENUM, [
   "toJSON", DateToJSON
 ]);
 
 })