Lock the prototype of internal classes.

src/date.js

 // Copyright 2006-2008 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 1030 matching lines @@
   // Reset the date cache:
   cache = Date_cache;
   cache.time = $NaN;
   cache.year = $NaN;
   cache.string = null;
 }
 
 
 // -------------------------------------------------------------------
 
-function SetupDate() {
-  // Setup non-enumerable properties of the Date object itself.
+function SetUpDate() {
+  %CheckIsBootstrapping();
+  // Set up non-enumerable properties of the Date object itself.
   InstallFunctions($Date, DONT_ENUM, $Array(
     "UTC", DateUTC,
     "parse", DateParse,
     "now", DateNow
   ));
 
-  // Setup non-enumerable constructor property of the Date prototype object.
+  // Set up non-enumerable constructor property of the Date prototype object.
   %SetProperty($Date.prototype, "constructor", $Date, DONT_ENUM);
 
-  // Setup non-enumerable functions of the Date prototype object and
+  // Set up non-enumerable functions of the Date prototype object and
   // set their names.
   InstallFunctionsOnHiddenPrototype($Date.prototype, DONT_ENUM, $Array(
     "toString", DateToString,
     "toDateString", DateToDateString,
     "toTimeString", DateToTimeString,
     "toLocaleString", DateToLocaleString,
     "toLocaleDateString", DateToLocaleDateString,
     "toLocaleTimeString", DateToLocaleTimeString,
     "valueOf", DateValueOf,
     "getTime", DateGetTime,
@@ skipping 31 matching lines @@
     "setUTCFullYear", DateSetUTCFullYear,
     "toGMTString", DateToGMTString,
     "toUTCString", DateToUTCString,
     "getYear", DateGetYear,
     "setYear", DateSetYear,
     "toISOString", DateToISOString,
     "toJSON", DateToJSON
   ));
 }
 
-SetupDate();
+SetUpDate();