Do not allow calls to SetProtoType on functions that should not have a protot...

src/accessors.cc

Index: src/accessors.cc
===================================================================
--- src/accessors.cc	(revision 6761)
+++ src/accessors.cc	(working copy)
@@ -447,6 +447,7 @@
   JSFunction* function = FindInPrototypeChain<JSFunction>(object, &found_it);
   if (!found_it) return Heap::undefined_value();
   if (!function->has_prototype()) {
+    if (!function->should_have_prototype()) return Heap::undefined_value();
     Object* prototype;
     { MaybeObject* maybe_prototype = Heap::AllocateFunctionPrototype(function);
       if (!maybe_prototype->ToObject(&prototype)) return maybe_prototype;