Remove the extensibility flag. Instead just rely on hidden_string as indication.

src/runtime.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 <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 5023 matching lines @@
   // to not worry about changing the instance_descriptor and creating a new
   // map.
   if (lookup.IsFound() &&
       (attr != lookup.GetAttributes() || lookup.IsPropertyCallbacks())) {
     // Use IgnoreAttributes version since a readonly property may be
     // overridden and SetProperty does not allow this.
     Handle<Object> result;
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, result,
         JSObject::SetOwnPropertyIgnoreAttributes(
-            js_object, name, obj_value, attr, PERFORM_EXTENSIBILITY_CHECK,
+            js_object, name, obj_value, attr,
             JSReceiver::MAY_BE_STORE_FROM_KEYED, JSObject::DONT_FORCE_FIELD));
     return *result;
   }
 
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       Runtime::DefineObjectProperty(
           js_object, name, obj_value, attr,
           JSReceiver::CERTAINLY_NOT_STORE_FROM_KEYED));
@@ skipping 133 matching lines @@
                                 SLOPPY, false, DEFINE_PROPERTY);
   }
 
   if (key->IsName()) {
     Handle<Name> name = Handle<Name>::cast(key);
     if (name->AsArrayIndex(&index)) {
       return JSObject::SetElement(js_object, index, value, attr,
                                   SLOPPY, false, DEFINE_PROPERTY);
     } else {
       if (name->IsString()) name = String::Flatten(Handle<String>::cast(name));
-      return JSObject::SetOwnPropertyIgnoreAttributes(
-          js_object, name, value, attr, PERFORM_EXTENSIBILITY_CHECK,
-          store_from_keyed);
+      return JSObject::SetOwnPropertyIgnoreAttributes(js_object, name, value,
+                                                      attr, store_from_keyed);
     }
   }
 
   // Call-back into JavaScript to convert the key to a string.
   Handle<Object> converted;
   ASSIGN_RETURN_ON_EXCEPTION(
       isolate, converted, Execution::ToString(isolate, key), Object);
   Handle<String> name = Handle<String>::cast(converted);
 
   if (name->AsArrayIndex(&index)) {
     return JSObject::SetElement(js_object, index, value, attr,
                                 SLOPPY, false, DEFINE_PROPERTY);
   } else {
-    return JSObject::SetOwnPropertyIgnoreAttributes(
-        js_object, name, value, attr, PERFORM_EXTENSIBILITY_CHECK,
-        store_from_keyed);
+    return JSObject::SetOwnPropertyIgnoreAttributes(js_object, name, value,
+                                                    attr, store_from_keyed);
   }
 }
 
 
 MaybeHandle<Object> Runtime::DeleteObjectProperty(Isolate* isolate,
                                                   Handle<JSReceiver> receiver,
                                                   Handle<Object> key,
                                                   JSReceiver::DeleteMode mode) {
   // Check if the given key is an array index.
   uint32_t index;
@@ skipping 10401 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal