def read_little_endian64(self):
        """Interprets the next 8 bytes of the stream as a little-endian
        encoded, unsiged 64-bit integer, and returns that integer.
        """
        try:
            i = struct.unpack(wire_format.FORMAT_UINT64_LITTLE_ENDIAN,
                              self._input.read(8))
            self._pos += 8
            return i[0]  # unpack() result is a 1-element tuple.
        except struct.error as e:
            raise errors.DecodeError(e)
Interprets the next 8 bytes of the stream as a little-endian
        encoded, unsiged 64-bit integer, and returns that integer.