Retrieves the MIME type of the resource pointed by @uri.
In the event the URI cannot be found, %NULL is returned and
@error is set to #G_BOOKMARK_FILE_ERROR_URI_NOT_FOUND. In the
event that the MIME type cannot be found, %NULL is returned and
@error is set to #G_BOOKMARK_FILE_ERROR_INVALID_VALUE.
Retrieves the MIME type of the resource pointed by @uri.
In the event the URI cannot be found, %NULL is returned and @error is set to #G_BOOKMARK_FILE_ERROR_URI_NOT_FOUND. In the event that the MIME type cannot be found, %NULL is returned and @error is set to #G_BOOKMARK_FILE_ERROR_INVALID_VALUE.