[runtime] Add PropertyConstness bit to PropertyDetails.

src/lookup.cc

 // Copyright 2014 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/lookup.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/elements.h"
 #include "src/field-type.h"
@@ skipping 669 matching lines @@
   if (IsElement()) {
     Handle<JSObject> object = Handle<JSObject>::cast(holder);
     ElementsAccessor* accessor = object->GetElementsAccessor();
     accessor->Set(object, number_, *value);
   } else if (holder->HasFastProperties()) {
     if (property_details_.location() == kField) {
       JSObject::cast(*holder)->WriteToField(descriptor_number(),
                                             property_details_, *value);
     } else {
       DCHECK_EQ(kDescriptor, property_details_.location());
+      DCHECK_EQ(kConst, property_details_.constness());
     }
   } else if (holder->IsJSGlobalObject()) {
     GlobalDictionary* dictionary = JSObject::cast(*holder)->global_dictionary();
     Object* cell = dictionary->ValueAt(dictionary_entry());
     DCHECK(cell->IsPropertyCell());
     PropertyCell::cast(cell)->set_value(*value);
   } else {
     NameDictionary* dictionary = holder->property_dictionary();
     dictionary->ValueAtPut(dictionary_entry(), *value);
   }
@@ skipping 172 matching lines @@
 
   // We have found a cached property! Modify the iterator accordingly.
   name_ = maybe_name.ToHandleChecked();
   Restart();
   CHECK_EQ(state(), LookupIterator::DATA);
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8