static readSize_(data, offset) {
    let size = 0;
    size = (data[offset] & 0x7f) << 21;
    size |= (data[offset + 1] & 0x7f) << 14;
    size |= (data[offset + 2] & 0x7f) << 7;
    size |= data[offset + 3] & 0x7f;
    return size;
  }
@param {Uint8Array} data
@param {number} offset
@return {number}
@private