Track up to 5 stable maps as field type.

src/objects-debug.cc

 // Copyright 2012 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 282 matching lines @@
     for (int i = 0; i < map()->NumberOfOwnDescriptors(); i++) {
       if (descriptors->GetDetails(i).type() == FIELD) {
         Representation r = descriptors->GetDetails(i).representation();
         int field = descriptors->GetFieldIndex(i);
         Object* value = RawFastPropertyAt(field);
         if (r.IsDouble()) ASSERT(value->IsHeapNumber());
         if (value->IsUninitialized()) continue;
         if (r.IsSmi()) ASSERT(value->IsSmi());
         if (r.IsHeapObject()) ASSERT(value->IsHeapObject());
         HeapType* field_type = descriptors->GetFieldType(i);
-        if (field_type->IsClass()) {
-          Map* map = *field_type->AsClass()->Map();
-          CHECK(!map->is_stable() || HeapObject::cast(value)->map() == map);
-        } else if (r.IsNone()) {
+        if (r.IsNone()) {
           CHECK(field_type->Is(HeapType::None()));
-        } else {
-          CHECK(HeapType::Any()->Is(field_type));
+        } else if (!HeapType::Any()->Is(field_type)) {
+          CHECK(!field_type->NowStable() || field_type->NowContains(value));
         }
       }
     }
   }
 
   // If a GC was caused while constructing this object, the elements
   // pointer may point to a one pointer filler map.
   if (ElementsAreSafeToExamine()) {
     CHECK_EQ((map()->has_fast_smi_or_object_elements() ||
               (elements() == GetHeap()->empty_fixed_array())),
@@ skipping 872 matching lines @@
   for (int i = 0; i < number_of_transitions(); ++i) {
     if (!CheckOneBackPointer(current_map, GetTarget(i))) return false;
   }
   return true;
 }
 
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal