opts.go
func HTTPClient(client *http.Client) Option {
	return func(sh *StackdriverHook) error {
		// create logging service
		l, err := logging.New(client)
		if err != nil {
			return err
		}
		// create error reporting service
		e, err := errorReporting.New(client)
		if err != nil {
			return err
		} else {
			ErrorService(e)
		}

		return LoggingService(l)(sh)
	}
}
func HTTPClient(client *http.Client) Option {
	return func(sh *StackdriverHook) error {
		// create logging service
		l, err := logging.New(client)
		if err != nil {
			return err
		}
		// create error reporting service
		e, err := errorReporting.New(client)
		if err != nil {
			return err
		} else {
			ErrorService(e)
		}

		return LoggingService(l)(sh)
	}
}
// HTTPClient is an option that sets the http.Client to be used when creating
// the Stackdriver service.