Call `Reload` on every `EventAccumulator`.

def Reload(self):
    """Call `Reload` on every `EventAccumulator`."""
    logger.info('Beginning EventMultiplexer.Reload()')
    self._reload_called = True
    # Build a list so we're safe even if the list of accumulators is modified
    # even while we're reloading.
    with self._accumulators_mutex:
      items = list(self._accumulators.items())

    names_to_delete = set()
    for name, accumulator in items:
      try:
        accumulator.Reload()
      except (OSError, IOError) as e:
        logger.error("Unable to reload accumulator '%s': %s", name, e)
      except directory_watcher.DirectoryDeletedError:
        names_to_delete.add(name)

    with self._accumulators_mutex:
      for name in names_to_delete:
        logger.warn("Deleting accumulator '%s'", name)
        del self._accumulators[name]
    logger.info('Finished with EventMultiplexer.Reload()')
    return self