Add missing comment from last commit.

src/serialize.h

 // Copyright 2006-2009 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 338 matching lines @@
   virtual void VisitPointers(Object** start, Object** end);
 
   virtual void VisitExternalReferences(Address* start, Address* end) {
     UNREACHABLE();
   }
 
   virtual void VisitRuntimeEntry(RelocInfo* rinfo) {
     UNREACHABLE();
   }
 
-  void ReadChunk(Object** start, Object** end, int space, Address address);
+  // 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
+  // of the object we are writing into, or NULL if we are not writing into an
+  // object, ie if we are writing a series of tagged values that are not on the
+  // heap.
+  void ReadChunk(
+      Object** start, Object** end, int space, Address object_address);
   HeapObject* GetAddressFromStart(int space);
   inline HeapObject* GetAddressFromEnd(int space);
   Address Allocate(int space_number, Space* space, int size);
   void ReadObject(int space_number, Space* space, Object** write_back);
 
   // Cached current isolate.
   Isolate* isolate_;
 
   // Keep track of the pages in the paged spaces.
   // (In large object space we are keeping track of individual objects
@@ skipping 268 matching lines @@
  private:
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     return false;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_