code: public VehicleDataSource addSource(VehicleDataSource source) {
          source.setCallback(this);
          mSources.add(source);
          if(isActive()) {
              source.onPipelineActivated();
          } else {
              source.onPipelineDeactivated();
          }
          return source;
      }
docs: Add a new source to the pipeline.
  
  The source is given a reference to this DataPipeline as its callback.