getSpecifiedWindowIds_(bitmap) {
    const ids = [];
    for (let i = 0; i < 8; i++) {
      const windowSpecified = (bitmap & 0x01) === 0x01;
      if (windowSpecified && this.windows_[i]) {
        ids.push(i);
      }
      bitmap >>= 1;
    }
    return ids;
  }
Yields each non-null window specified in the 8-bit bitmap.
@param {number} bitmap 8 bits corresponding to each of the 8 windows.
@return {!Array<number>}
@private