From given mode name, return mode file path from
        ``settings.CODEMIRROR_MODES`` map.

        Arguments:
            name (string): Mode name.

        Raises:
            KeyError: When given name does not exist in
                ``settings.CODEMIRROR_MODES``.

        Returns:
            string: Mode file path.

def resolve_mode(self, name):
        """
        From given mode name, return mode file path from
        ``settings.CODEMIRROR_MODES`` map.

        Arguments:
            name (string): Mode name.

        Raises:
            KeyError: When given name does not exist in
                ``settings.CODEMIRROR_MODES``.

        Returns:
            string: Mode file path.
        """
        if name not in settings.CODEMIRROR_MODES:
            msg = ("Given config name '{}' does not exists in "
                   "'settings.CODEMIRROR_MODES'.")
            raise UnknowModeError(msg.format(name))

        return settings.CODEMIRROR_MODES.get(name)