message: Fix the memory size computation
  Summary: Make sure you include the header size.
diff: @@ -282,7 +282,7 @@ impl Arena {
  .entry(x.dupe())
  .or_insert_with(|| (v.get_type(), (0, 0)));
  e.1.0 += 1;
  - e.1.1 += v.memory_size() + v.extra_memory();
  + e.1.1 += mem::size_of::<AValueHeader>() + v.memory_size() + v.extra_memory();
  };
  for_each(&self.drop, &mut f);
  for_each(&self.non_drop, &mut f);
  @@ -476,6 +476,8 @@ mod test {
  arena.alloc(mk_str("test"));
  let res = arena.allocated_summary().summary;
  assert_eq!(res.len(), 1);
  - assert_eq!(res.values().next().unwrap().0, 2);
  + let entry = res.values().next().unwrap();
  + assert_eq!(entry.0, 2);
  + assert_eq!(entry.1, arena.allocated_bytes())
  }
  }
  