function requestTiles(tileset) {
  const requestedTiles = tileset._requestedTiles;
  requestedTiles.sort(sortTilesByPriority);
  for (let i = 0; i < requestedTiles.length; ++i) {
    requestContent(tileset, requestedTiles[i]);
  }
}
Sort requests by priority before making any requests.
This makes it less likely that requests will be cancelled after being issued.
@private
@param {Cesium3DTileset} tileset