Fix another corner-case behavior of Object::SetSuperProperty.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 7422aec4e6603ddbbf52a3295a9fea13e8da9b6b..f3cccc078e2aeffd3b0f71ef416c07341ea1dbde 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -3765,12 +3765,19 @@ Maybe<bool> Object::SetSuperProperty(LookupIterator* it, Handle<Object> value,
                                             should_throw);
 
       case LookupIterator::DATA: {
+        DCHECK(it->GetReceiver()->IsJSObject());
         PropertyDetails details = own_lookup.property_details();
-        if (details.IsConfigurable() || !details.IsReadOnly()) {
-          return JSObject::DefineOwnPropertyIgnoreAttributes(
-              &own_lookup, value, details.attributes(), should_throw);
+        if (details.IsReadOnly()) {
+          return WriteToReadOnlyProperty(&own_lookup, value, should_throw);
         }
-        return WriteToReadOnlyProperty(&own_lookup, value, should_throw);
+        if (!JSObject::IsExtensible(

[rossberg, 2015/11/03 10:55:11]

I don't think this check is correct. Extensibility doesn't matter if the
property already exists.

+                Handle<JSObject>::cast(it->GetReceiver()))) {
+          RETURN_FAILURE(it->isolate(), should_throw,
+                         NewTypeError(MessageTemplate::kObjectNotExtensible,
+                                      it->GetName()));
+        }
+        return JSObject::DefineOwnPropertyIgnoreAttributes(
+            &own_lookup, value, details.attributes(), should_throw);
       }
 
       case LookupIterator::ACCESSOR: {