Don't unmark dictionary mode maps as unstable.

src/objects-inl.h

 // Copyright 2012 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 3970 matching lines @@
   set_bit_field3(IsShared::update(bit_field3(), value));
 }
 
 
 bool Map::is_shared() {
   return IsShared::decode(bit_field3());
 }
 
 
 void Map::set_dictionary_map(bool value) {
-  if (value) mark_unstable();
-  set_bit_field3(DictionaryMap::update(bit_field3(), value));
+  uint32_t new_bit_field3 = DictionaryMap::update(bit_field3(), value);
+  new_bit_field3 = IsUnstable::update(new_bit_field3, value);
+  set_bit_field3(new_bit_field3);
 }
 
 
 bool Map::is_dictionary_map() {
   return DictionaryMap::decode(bit_field3());
 }
 
 
 Code::Flags Code::flags() {
   return static_cast<Flags>(READ_INT_FIELD(this, kFlagsOffset));
@@ skipping 2801 matching lines @@
 #undef READ_UINT32_FIELD
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_