shiftLeft(numBits) {
    numBits &= 63;
    if (numBits == 0) {
      return this;
    } else {
      var low = this.low_;
      if (numBits < 32) {
        var high = this.high_;
        return Long.fromBits(
            low << numBits, (high << numBits) | (low >>> (32 - numBits)));
      } else {
        return Long.fromBits(0, low << (numBits - 32));
      }
    }
  }
Returns this Long with bits shifted to the left by the given amount.
@param {number} numBits The number of bits by which to shift.
@return {!Long} This shifted to the left by the given amount.