static fromBits(lowBits, highBits) {
    return new Long(lowBits, highBits);
  }
Returns a Long representing the 64-bit integer that comes by concatenating
the given high and low bits.  Each is assumed to use 32 bits.
@param {number} lowBits The low 32-bits.
@param {number} highBits The high 32-bits.
@return {!Long} The corresponding Long value.