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

src/full-codegen.cc

Index: src/full-codegen.cc
diff --git a/src/full-codegen.cc b/src/full-codegen.cc
index fc7b6899bcbffb29127b009fe5ffceff22ff3908..0f44cf233ea9efc1497ff78c151ae08bf6b82ede 100644
--- a/src/full-codegen.cc
+++ b/src/full-codegen.cc
@@ -584,6 +584,15 @@ void FullCodeGenerator::VisitDeclarations(
 }
 
 
+int FullCodeGenerator::DeclareGlobalsFlags() {
+  int flags = 0;
+  if (is_eval()) flags |= kDeclareGlobalsEvalFlag;
+  if (is_strict_mode()) flags |= kDeclareGlobalsStrictModeFlag;
+  if (is_native()) flags |= kDeclareGlobalsNativeFlag;
+  return flags;
+}
+
+
 void FullCodeGenerator::SetFunctionPosition(FunctionLiteral* fun) {
   CodeGenerator::RecordPositions(masm_, fun->start_position());
 }