Convert an integer to a varint and write it using the write function.

def VarintEncode(value):
  """Convert an integer to a varint and write it using the write function."""
  result = b""
  if value < 0:
    raise ValueError("Varint can not encode a negative number.")

  bits = value & 0x7f
  value >>= 7

  while value:
    result += HIGH_CHR_MAP[bits]
    bits = value & 0x7f
    value >>= 7

  result += CHR_MAP[bits]

  return result