Use null instead of undefined for deleted elements in code caches....

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 1425 matching lines @@
 
 class FixedArray: public Array {
  public:
 
   // Setter and getter for elements.
   inline Object* get(int index);
   inline void set(int index, Object* value);
 
   // Setters for frequently used oddballs located in old space.
   inline void set_undefined(int index);
+  inline void set_null(int index);
   inline void set_the_hole(int index);
 
   // Setter that skips the write barrier if mode is SKIP_WRITE_BARRIER.
   enum WriteBarrierMode { SKIP_WRITE_BARRIER, UPDATE_WRITE_BARRIER };
   inline void set(int index, Object* value, WriteBarrierMode mode);
   // Return the write barrier mode for this.
   inline WriteBarrierMode GetWriteBarrierMode();
 
   // Copy operations.
   Object* Copy();
@@ skipping 2406 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_