Add missing checks for failure after AddElementsTransition.

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 4728 matching lines @@
 
   // Returns the map that this map transitions to if its elements_kind
   // is changed to |elements_kind|, or NULL if no such map is cached yet.
   // |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);
+  MUST_USE_RESULT 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 handle if no match is
   // found at all.
   Handle<Map> FindTransitionedMap(MapHandleList* candidates);
   Map* FindTransitionedMap(MapList* candidates);
 
 
   // Dispatched behavior.
 #ifdef OBJECT_PRINT
@@ skipping 3538 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_