Specify connection timing for HTTP/3

Closes w3c/navigation-timing#165.

Co-authored-by: Anne van Kesteren <[email protected]>

Author: noamr

fetch.bs

@@ -2645,6 +2645,12 @@ boolean <var>http3Only</var>, run these steps:
  <a for="connection timing info">secure connection start time</a> should be the result of calling
  <a for=/>unsafe shared current time</a> immmediately before starting the handshake process to
  secure <var>connection</var>. [[!TLS]]
+
+ <li><p>If <var>connection</var> is an HTTP/3 connection, <var>timingInfo</var>'s
+ <a for="connection timing info">connection start time</a> and <var>timingInfo</var>'s
+ <a for="connection timing info">secure connection start time</a> must be equal. (In HTTP/3
+ the secure transport handshake process is performed as part of the initial connection setup.)
+ [[!HTTP3]]
 </ul>
 
 <p class=note>The <a for=/>clamp and coarsen connection timing info</a> algorithm ensures that