code: public <R extends RequestQueue> R addMarker(String tag, Object... args) {
          Marker marker = new Marker(tag,
                  Thread.currentThread().getId(),
                  Thread.currentThread().getName(),
                  System.nanoTime());
          for (RequestListener.MarkerListener markerListener : markerListeners) {
              markerListener.onMarker(marker, args);
          }
          return (R) this;
      }
docs: Adds a marker for the {@link RequestQueue}
  @param tag
  @param args
  @param <R>
  @return