code: public synchronized void executeTaskWithUnifiedListener(@NonNull DownloadTask task,
                                                              @NonNull DownloadListener listener) {
          attachListener(task, listener);
  
          task.execute(hostListener);
      }
docs: Attach the {@code listener} to this manager and execute the {@code task}.
  
  @param task     the task will be execute.
  @param listener the listener will be attached to this manager.