t1.TLSClientConfig.NextProtos = append(t1.TLSClientConfig.NextProtos, "http/1.1")
	}
	upgradeFn := func(authority string, c *tls.Conn) RoundTripper {
		addr := http2authorityAddr("https", authority)
		if used, err := connPool.addConnIfNeeded(addr, t2, c); err != nil {
			go c.Close()
			return http2erringRoundTripper{err}
		} else if !used {
			// Turns out we don't need this c.