Suspicious logic in XtraDB extra slow log stats collection

innobase_trx_init() enables stats collection just based on the log_slow_verbosity=innodb:

#ifdef EXTENDED_SLOWLOG
 if (thd_log_slow_verbosity(thd) & (1ULL << SLOG_V_INNODB)) {
  trx->take_stats = TRUE;
 } else {
  trx->take_stats = FALSE;
 }
#else
 trx->take_stats = FALSE;
#endif

Then all the code that wants to update stats check if both the slow log is enabled and trx->take_stats is TRUE:

  if (innobase_get_slow_log() && trx && trx->take_stats && start_time)
  {
   ut_usectime(&sec, &ms);
   finish_time = (ib_uint64_t)sec * 1000000 + ms;
   trx->io_reads_wait_timer += (ulint)(finish_time - start_time);
  }

Why don't we check if the slow log is enabled before setting trx->take_stats? The only downside is a rather pathological case when we have long running transactions, and want to collect stats for them with log_slow_verbosity=innodb without writing to the slow log, and then want all previously collected stats to be reflected in the slow log once it is enabled in the middle of those long-runnign transactions.

The upside is that we would also remove calls to to innobase_get_slow_log(), which are in some cases on critical code paths.