code: private Set<Integer> findExpiredIndexesBeforeIndex(int index) {
  		long indexTime = getLineTime(index);
  		Set<Integer> removeThese = Sets.newHashSet();
  		for (int i = index - 1; i >= 0; i--) {
  			if (indexTime - getLineTime(i) > MAXIMUM_ARRIVAL_TIME_DIFFERENCE_MS) {
  				listener.timestampNotFound(getLine(i), getLineTime(i));
  				removeThese.add(i);
  			}
  		}
  		return removeThese;
  	}
docs: Returns the list of those indexes that can be removed from the buffer
  because they have a timestamp more than
  MAXIMUM_ARRIVAL_TIME_DIFFERENCE_MS from the arrival time of the given
  index.
  
  @param index
  @return