Map::ReconfigureProperty() should mark map as unstable when it returns a different map.

src/objects-printer.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/disasm.h"
 #include "src/disassembler.h"
 #include "src/heap/objects-visiting.h"
 #include "src/jsregexp.h"
@@ skipping 398 matching lines @@
 void Map::MapPrint(std::ostream& os) {  // NOLINT
   HeapObject::PrintHeader(os, "Map");
   os << " - type: " << TypeToString(instance_type()) << "\n";
   os << " - instance size: " << instance_size() << "\n";
   os << " - inobject properties: " << inobject_properties() << "\n";
   os << " - elements kind: " << ElementsKindToString(elements_kind());
   os << "\n - pre-allocated property fields: "
      << pre_allocated_property_fields() << "\n";
   os << " - unused property fields: " << unused_property_fields() << "\n";
   if (is_deprecated()) os << " - deprecated_map\n";
+  if (is_stable()) os << " - stable_map\n";
   if (is_dictionary_map()) os << " - dictionary_map\n";
   if (is_prototype_map()) {
     os << " - prototype_map\n";
     os << " - prototype info: " << Brief(prototype_info());
   } else {
     os << " - back pointer: " << Brief(GetBackPointer());
   }
   if (is_hidden_prototype()) os << " - hidden_prototype\n";
   if (has_named_interceptor()) os << " - named_interceptor\n";
   if (has_indexed_interceptor()) os << " - indexed_interceptor\n";
@@ skipping 742 matching lines @@
   }
 }
 
 
 void JSObject::PrintTransitions(std::ostream& os) {  // NOLINT
   TransitionArray::PrintTransitions(os, map()->raw_transitions());
 }
 #endif  // defined(DEBUG) || defined(OBJECT_PRINT)
 }  // namespace internal
 }  // namespace v8