Simplify ObjectVisitor for external references.

src/serialize.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 321 matching lines @@
 
   void set_reservation(int space_number, int reservation) {
     ASSERT(space_number >= 0);
     ASSERT(space_number <= LAST_SPACE);
     reservations_[space_number] = reservation;
   }
 
  private:
   virtual void VisitPointers(Object** start, Object** end);
 
-  virtual void VisitExternalReferences(Address* start, Address* end) {
-    UNREACHABLE();
-  }
-
   virtual void VisitRuntimeEntry(RelocInfo* rinfo) {
     UNREACHABLE();
   }
 
   // Allocation sites are present in the snapshot, and must be linked into
   // a list at deserialization time.
   void RelinkAllocationSite(AllocationSite* site);
 
   // Fills in some heap data in an area from start to end (non-inclusive).  The
   // space id is used for the write barrier.  The object_address is the address
@@ skipping 158 matching lines @@
       : serializer_(serializer),
         object_(HeapObject::cast(o)),
         sink_(sink),
         reference_representation_(how_to_code + where_to_point),
         bytes_processed_so_far_(0),
         code_object_(o->IsCode()),
         code_has_been_output_(false) { }
     void Serialize();
     void VisitPointers(Object** start, Object** end);
     void VisitEmbeddedPointer(RelocInfo* target);
-    void VisitExternalReferences(Address* start, Address* end);
+    void VisitExternalReference(Address* p);
     void VisitExternalReference(RelocInfo* rinfo);
     void VisitCodeTarget(RelocInfo* target);
     void VisitCodeEntry(Address entry_address);
     void VisitCell(RelocInfo* rinfo);
     void VisitRuntimeEntry(RelocInfo* reloc);
     // Used for seralizing the external strings that hold the natives source.
     void VisitExternalAsciiString(
         v8::String::ExternalAsciiStringResource** resource);
     // We can't serialize a heap with external two byte strings.
     void VisitExternalTwoByteString(
@@ skipping 132 matching lines @@
  private:
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     return false;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_