code: void addUnchecked(final BaseDownloadTask.IRunningTask task) {
          if (task.isMarkedAdded2List()) {
              return;
          }
  
          synchronized (mList) {
              if (mList.contains(task)) {
                  FileDownloadLog.w(this, "already has %s", task);
              } else {
                  task.markAdded2List();
                  mList.add(task);
                  if (FileDownloadLog.NEED_LOG) {
                      FileDownloadLog.v(this, "add list in all %s %d %d", task,
                              task.getOrigin().getStatus(), mList.size());
                  }
              }
          }
      }
docs: This method generally used for enqueuing the task which will be assembled by a queue.
  
  @see BaseDownloadTask.InQueueTask#enqueue()