Make sure builtin functions don't rely on __proto__.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 7e53c68b8282e181e7c8da9e4410583947d605c7..5dc767f71f22e2dab643d73472810ff4db7fefb8 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4852,7 +4852,7 @@ class Map: public HeapObject {
   inline bool function_with_prototype();
 
   // Tells whether the instance with this map should be ignored by the
-  // __proto__ accessor.
+  // Object.getPrototypeOf() function and the __proto__ accessor.
   inline void set_is_hidden_prototype() {
     set_bit_field(bit_field() | (1 << kIsHiddenPrototype));
   }