[runtime] Add PropertyConstness bit to PropertyDetails.

src/map-updater.h

 // Copyright 2017 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.
 
 #ifndef V8_MAP_RECONFIGURER_H_
 #define V8_MAP_RECONFIGURER_H_
 
 #include "src/elements-kind.h"
 #include "src/globals.h"
 #include "src/handles.h"
@@ skipping 139 matching lines @@
   int old_nof_;
 
   State state_ = kInitialized;
   ElementsKind new_elements_kind_;
 
   // If |modified_descriptor_| is not equal to -1 them the fields below form
   // an "update" of the |old_map_|'s descriptors.
   int modified_descriptor_ = -1;
   PropertyKind new_kind_ = kData;
   PropertyAttributes new_attributes_ = NONE;
+  PropertyConstness new_constness_ = kMutable;
   PropertyLocation new_location_ = kField;
   Representation new_representation_ = Representation::None();
 
   // Data specific to kField location.
   Handle<FieldType> new_field_type_;
 
   // Data specific to kDescriptor location.
   Handle<Object> new_value_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MAP_RECONFIGURER_H_