addLocation(streamId, pathwayId, uri) {
    let streamLocations = this.locations_.get(streamId);
    if (!streamLocations) {
      streamLocations = new Map();
    }
    streamLocations.set(pathwayId, uri);
    this.locations_.set(streamId, streamLocations);
  }
@param {string|number} streamId
@param {string} pathwayId
@param {string} uri