Lock the prototype of internal classes.

src/regexp.js

 // Copyright 2006-2009 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 387 matching lines @@
 );
 
 // Override last match info with an array of actual substrings.
 // Used internally by replace regexp with function.
 // The array has the format of an "apply" argument for a replacement
 // function.
 var lastMatchInfoOverride = null;
 
 // -------------------------------------------------------------------
 
-function SetupRegExp() {
+function SetUpRegExp() {
+  %CheckIsBootstrapping();
   %FunctionSetInstanceClassName($RegExp, 'RegExp');
   %FunctionSetPrototype($RegExp, new $Object());
   %SetProperty($RegExp.prototype, 'constructor', $RegExp, DONT_ENUM);
   %SetCode($RegExp, RegExpConstructor);
 
   InstallFunctions($RegExp.prototype, DONT_ENUM, $Array(
     "exec", RegExpExec,
     "test", RegExpTest,
     "toString", RegExpToString,
     "compile", CompileRegExp
@@ skipping 58 matching lines @@
   %DefineAccessor($RegExp, 'rightContext', SETTER, NoOpSetter, DONT_DELETE);
   %DefineAccessor($RegExp, "$'", GETTER, RegExpGetRightContext, DONT_ENUM | DONT_DELETE);
   %DefineAccessor($RegExp, "$'", SETTER, NoOpSetter, DONT_ENUM | DONT_DELETE);
 
   for (var i = 1; i < 10; ++i) {
     %DefineAccessor($RegExp, '$' + i, GETTER, RegExpMakeCaptureGetter(i), DONT_DELETE);
     %DefineAccessor($RegExp, '$' + i, SETTER, NoOpSetter, DONT_DELETE);
   }
 }
 
-
-SetupRegExp();
+SetUpRegExp();