func (v *Surface) GetMimeData(mimeType MimeType) []byte {
	cstr := C.CString(string(mimeType))
	defer C.free(unsafe.Pointer(cstr))
	var data *C.uchar
	var length C.ulong
	C.cairo_surface_get_mime_data(v.native(), cstr, &data, &length)
	return C.GoBytes(unsafe.Pointer(data), C.int(length))
}
func (v *Surface) GetMimeData(mimeType MimeType) []byte {
	cstr := C.CString(string(mimeType))
	defer C.free(unsafe.Pointer(cstr))
	var data *C.uchar
	var length C.ulong
	C.cairo_surface_get_mime_data(v.native(), cstr, &data, &length)
	return C.GoBytes(unsafe.Pointer(data), C.int(length))
}
// TODO(jrick) SetMimeData (depends on DestroyFunc)
// GetMimeData is a wrapper around cairo_surface_get_mime_data().  The
// returned mimetype data is returned as a Go byte slice.