loadMoreTiles(maxTotalLoading, maxNewLoads) {
    let newLoads = 0;
    while (
      this.tilesLoading_ < maxTotalLoading &&
      newLoads < maxNewLoads &&
      this.getCount() > 0
    ) {
      const tile = this.dequeue()[0];
      const tileKey = tile.getKey();
      const state = tile.getState();
      if (state === TileState.IDLE && !(tileKey in this.tilesLoadingKeys_)) {
        this.tilesLoadingKeys_[tileKey] = true;
        ++this.tilesLoading_;
        ++newLoads;
        tile.load();
      }
    }
  }
@param {number} maxTotalLoading Maximum number tiles to load simultaneously.
@param {number} maxNewLoads Maximum number of new tiles to load.