Introduce HTransitionElementsKind instruction.

src/objects.h

 // Copyright 2011 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 1771 matching lines @@
   MUST_USE_RESULT MaybeObject* ReplaceSlowProperty(
       String* name,
       Object* value,
       PropertyAttributes attributes);
 
   // Returns a new map with all transitions dropped from the object's current
   // map and the ElementsKind set.
   MUST_USE_RESULT MaybeObject* GetElementsTransitionMap(
       ElementsKind elements_kind);
 
+  MUST_USE_RESULT MaybeObject* TransitionElementsKind(ElementsKind to_kind);
+
+  static bool IsValidElementsTransition(ElementsKind from_kind,
+                                        ElementsKind to_kind);
+
   // Converts a descriptor of any other type to a real field,
   // backed by the properties array.  Descriptors of visible
   // types, such as CONSTANT_FUNCTION, keep their enumeration order.
   // Converts the descriptor on the original object's map to a
   // map transition, and the the new field is on the object's new map.
   MUST_USE_RESULT MaybeObject* ConvertDescriptorToFieldAndMapTransition(
       String* name,
       Object* new_value,
       PropertyAttributes attributes);
 
@@ skipping 2479 matching lines @@
   // |safe_to_add_transitions| is set to false if adding transitions is not
   // allowed.
   Map* LookupElementsTransitionMap(ElementsKind elements_kind,
                                    bool* safe_to_add_transition);
 
   // Adds an entry to this map's descriptor array for a transition to
   // |transitioned_map| when its elements_kind is changed to |elements_kind|.
   MaybeObject* AddElementsTransition(ElementsKind elements_kind,
                                      Map* transitioned_map);
 
+  // Returns the transitioned map for this map with the most generic
+  // elements_kind that's found in |candidates|, or NULL if no match is
+  // found at all.
+  Map* FindTransitionedMap(MapList* candidates);
+
   // Dispatched behavior.
 #ifdef OBJECT_PRINT
   inline void MapPrint() {
     MapPrint(stdout);
   }
   void MapPrint(FILE* out);
 #endif
 #ifdef DEBUG
   void MapVerify();
   void SharedMapVerify();
@@ skipping 3288 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_