appengine.go
func APICall(ctx context.Context, service, method string, in, out proto.Message) error {
	return internal.Call(ctx, service, method, in, out)
}
func APICall(ctx context.Context, service, method string, in, out proto.Message) error {
	return internal.Call(ctx, service, method, in, out)
}
// APICall performs an API call.
//
// This is not intended for general use; it is exported for use in conjunction
// with WithAPICallFunc.