Only remove the code object that caused the monomorphic prototype...

src/objects.h

 // Copyright 2006-2008 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 2325 matching lines @@
 
   // Clears the code cache.
   inline void ClearCodeCache();
 
   // Update code cache.
   Object* UpdateCodeCache(String* name, Code* code);
 
   // Returns the found code or undefined if absent.
   Object* FindInCodeCache(String* name, Code::Flags flags);
 
-  // Tells whether code is in the code cache.
-  bool IncludedInCodeCache(Code* code);
+  // Returns the non-negative index of the code object if it is in the
+  // cache and -1 otherwise.
+  int IndexInCodeCache(Code* code);
+
+  // Removes a code object from the code cache at the given index.
+  void RemoveFromCodeCache(int index);
 
   // Dispatched behavior.
   void MapIterateBody(ObjectVisitor* v);
 #ifdef DEBUG
   void MapPrint();
   void MapVerify();
 #endif
 
   // Layout description.
   static const int kInstanceAttributesOffset = HeapObject::kSize;
@@ skipping 1499 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_