Combine %_SubString and %_StringCharAt.

src/json.js

 // Copyright 2009 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 175 matching lines @@
     // Unwrap 'space' if it is wrapped
     if (IS_NUMBER_WRAPPER(space)) {
       space = ToNumber(space);
     } else if (IS_STRING_WRAPPER(space)) {
       space = ToString(space);
     }
   }
   var gap;
   if (IS_NUMBER(space)) {
     space = MathMax(0, MathMin(ToInteger(space), 10));
-    gap = SubString("          ", 0, space);
+    gap = %_SubString("          ", 0, space);
   } else if (IS_STRING(space)) {
     if (space.length > 10) {
-      gap = SubString(space, 0, 10);
+      gap = %_SubString(space, 0, 10);
     } else {
       gap = space;
     }
   } else {
     gap = "";
   }
   return JSONSerialize('', {'': value}, replacer, new InternalArray(), "", gap);
 }
 
 
 function SetUpJSON() {
   %CheckIsBootstrapping();
   InstallFunctions($JSON, DONT_ENUM, $Array(
     "parse", JSONParse,
     "stringify", JSONStringify
   ));
 }
 
 
 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, void 0, new InternalArray(), "", "");
 }
 
 SetUpJSON();