code: @Override
      public void registerBroadcastListener(String broadcastName, BroadcastListener broadcastListener) {
          broadcastListeners.putIfAbsent(broadcastName, new ArrayList<BroadcastListener>());
          List<BroadcastListener> listeners = broadcastListeners.get(broadcastName);
          synchronized (listeners) {
              listeners.add(broadcastListener);
          }
      }
docs: Registers a broadcast listener that gets notified in case the broadcast
  is fired.
  
  @param broadcastName     the broadcast name as defined in the Franca model
  to subscribe to.
  @param broadcastListener the listener to add.