function updatePendingRequests(multipleContents, deltaRequestCount) {
  multipleContents._requestsInFlight += deltaRequestCount;
  multipleContents.tileset.statistics.numberOfPendingRequests +=
    deltaRequestCount;
}
Get an array of the inner content URLs, regardless of whether they've
been fetched or not. This is intended for use with
{@link Cesium3DTileset#debugShowUrl}.
@memberof Multiple3DTileContent.prototype

@type {string[]}
@readonly
@private