Support merging with distinct attributes.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 7273 matching lines @@
   for (descriptor = 0; descriptor < verbatim; descriptor++) {
     if (GetDetails(descriptor).type() == FIELD) current_offset++;
     result->CopyFrom(descriptor, this, descriptor, witness);
   }
 
   // |verbatim| -> |valid|
   for (; descriptor < valid; descriptor++) {
     Name* key = GetKey(descriptor);
     PropertyDetails details = GetDetails(descriptor);
     PropertyDetails other_details = other->GetDetails(descriptor);
-    ASSERT(details.attributes() == other_details.attributes());
 
     if (details.type() == FIELD || other_details.type() == FIELD ||
         (details.type() == CONSTANT_FUNCTION &&
          other_details.type() == CONSTANT_FUNCTION &&
          GetValue(descriptor) != other->GetValue(descriptor))) {
       Representation representation =
           details.representation().generalize(other_details.representation());
       FieldDescriptor d(key,
                         current_offset++,
-                        details.attributes(),
+                        other_details.attributes(),
                         representation);
       result->Set(descriptor, &d, witness);
     } else {
       result->CopyFrom(descriptor, other, descriptor, witness);
     }
   }
 
   // |valid| -> |new_size|
   for (; descriptor < new_size; descriptor++) {
     PropertyDetails details = other->GetDetails(descriptor);
@@ skipping 7820 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal