Make functions on the built-in object non-writable.

src/full-codegen.h

 // Copyright 2011 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 340 matching lines @@
   void VisitForControl(Expression* expr,
                        Label* if_true,
                        Label* if_false,
                        Label* fall_through) {
     TestContext context(this, expr, if_true, if_false, fall_through);
     VisitInCurrentContext(expr);
   }
 
   void VisitDeclarations(ZoneList<Declaration*>* declarations);
   void DeclareGlobals(Handle<FixedArray> pairs);
+  int DeclareGlobalsFlags();
 
   // Try to perform a comparison as a fast inlined literal compare if
   // the operands allow it.  Returns true if the compare operations
   // has been matched and all code generated; false otherwise.
   bool TryLiteralCompare(CompareOperation* compare,
                          Label* if_true,
                          Label* if_false,
                          Label* fall_through);
 
   // Platform-specific code for comparing the type of a value with
@@ skipping 177 matching lines @@
 #endif  // V8_TARGET_ARCH_IA32
 
   MacroAssembler* masm() { return masm_; }
 
   class ExpressionContext;
   const ExpressionContext* context() { return context_; }
   void set_new_context(const ExpressionContext* context) { context_ = context; }
 
   Handle<Script> script() { return info_->script(); }
   bool is_eval() { return info_->is_eval(); }
+  bool is_native() { return info_->is_native(); }
   bool is_strict_mode() { return function()->strict_mode(); }
   StrictModeFlag strict_mode_flag() {
     return is_strict_mode() ? kStrictMode : kNonStrictMode;
   }
   FunctionLiteral* function() { return info_->function(); }
   Scope* scope() { return scope_; }
 
   static Register result_register();
   static Register context_register();
 
@@ skipping 234 matching lines @@
 
   friend class NestedStatement;
 
   DISALLOW_COPY_AND_ASSIGN(FullCodeGenerator);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FULL_CODEGEN_H_