Register this descriptor with the Proto Struct.

def AddDescriptor(cls, field_desc):
    """Register this descriptor with the Proto Struct."""
    if not isinstance(field_desc, ProtoType):
      raise type_info.TypeValueError(
          "%s field '%s' should be of type ProtoType" %
          (cls.__name__, field_desc.name))

    # Ensure the field descriptor knows the class that owns it.
    field_desc.SetOwner(cls)

    # If the field is late bound we do not really add it to the descriptor set
    # yet. We must wait for the LateBindingPlaceHolder() to add it later.
    if field_desc.late_bound:
      # Keep track of unbound fields.
      cls.late_bound_type_infos[field_desc.name] = field_desc
      return

    # Ensure this field number is unique:
    if field_desc.field_number in cls.type_infos_by_field_number:
      raise type_info.TypeValueError(
          "Field number %s for field %s is not unique in %s" %
          (field_desc.field_number, field_desc.name, cls.__name__))

    # We store an index of the type info by tag values to speed up parsing.
    cls.type_infos_by_field_number[field_desc.field_number] = field_desc
    cls.type_infos_by_encoded_tag[field_desc.encoded_tag] = field_desc

    cls.type_infos.Append(field_desc)
    cls.late_bound_type_infos.pop(field_desc.name, None)

    # Add direct accessors only if the class does not already have them.
    if not hasattr(cls, field_desc.name):
      # This lambda is a class method so pylint: disable=protected-access
      # This is much faster than __setattr__/__getattr__
      setattr(
          cls, field_desc.name,
          property(lambda self: self.Get(field_desc.name), lambda self, x: self.
                   _Set(x, field_desc), None, field_desc.description))