Mark as prototype only after instantiating the function

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 4433 matching lines @@
   } else {
     set_bit_field2(bit_field2() & ~(1 << kIsExtensible));
   }
 }
 
 bool Map::is_extensible() {
   return ((1 << kIsExtensible) & bit_field2()) != 0;
 }
 
 
-void Map::mark_prototype_map() {
-  set_bit_field2(IsPrototypeMapBits::update(bit_field2(), true));
+void Map::set_is_prototype_map(bool value) {
+  set_bit_field2(IsPrototypeMapBits::update(bit_field2(), value));
 }
 
 bool Map::is_prototype_map() {
   return IsPrototypeMapBits::decode(bit_field2());
 }
 
 
 void Map::set_is_shared(bool value) {
   set_bit_field3(IsShared::update(bit_field3(), value));
 }
@@ skipping 1467 matching lines @@
 
 ACCESSORS(JSFunction, prototype_or_initial_map, Object,
           kPrototypeOrInitialMapOffset)
 
 
 Map* JSFunction::initial_map() {
   return Map::cast(prototype_or_initial_map());
 }
 
 
-void JSFunction::set_initial_map(Map* value) {
-  set_prototype_or_initial_map(value);
-}
-
-
 bool JSFunction::has_initial_map() {
   return prototype_or_initial_map()->IsMap();
 }
 
 
 bool JSFunction::has_instance_prototype() {
   return has_initial_map() || !prototype_or_initial_map()->IsTheHole();
 }
 
 
@@ skipping 1333 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_