Track up to 5 stable maps as field type.

src/objects.h

 // 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 6234 matching lines @@
 
   inline int GetInObjectPropertyOffset(int index);
 
   int NumberOfFields();
 
   bool InstancesNeedRewriting(Map* target,
                               int target_number_of_fields,
                               int target_inobject,
                               int target_unused);
   static Handle<Map> GeneralizeAllFieldRepresentations(Handle<Map> map);
-  static Handle<HeapType> GeneralizeFieldType(Handle<HeapType> old_field_type,
-                                              Handle<HeapType> new_field_type,
+  static Handle<HeapType> GeneralizeFieldType(Handle<HeapType> type1,
+                                              Handle<HeapType> type2,
                                               Isolate* isolate)
       V8_WARN_UNUSED_RESULT;
   static void GeneralizeFieldType(Handle<Map> map,
                                   int modify_index,
                                   Handle<HeapType> new_field_type);
   static Handle<Map> GeneralizeRepresentation(
       Handle<Map> map,
       int modify_index,
       Representation new_representation,
       Handle<HeapType> new_field_type,
@@ skipping 4833 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_