Add a timestamp to NavigationInfo (#346)

This ensures that navigation events get a (wall clock) timestamp.

Co-authored-by: Henrik Skupin <mail@hskupin.info>

Author: jgraham

index.bs

@@ -2824,6 +2824,7 @@ TODO: Link to the definition in the HTML spec.
 browsingContext.NavigationInfo = {
   context: browsingContext.BrowsingContext,
   navigation: browsingContext.Navigation / null,
+  timestamp: js-uint,
   url: text,
 }
 </pre>
@@ -2837,13 +2838,15 @@ To <dfn>get the navigation info</dfn>, given |context| and |navigation status|:
 
 1. Let |navigation id| be |navigation status|'s id.
 
+1. Let |timestamp| be a [=time value=] representing the current date and time in UTC.
+
 1. Let |url| be |navigation status|'s url.
 
-1. Return a [=map=] matching the
-   <code>browsingContext.NavigationInfo</code> production, with the
-   <code>context</code> field set to |context id|, the <code>navigation</code>
-   field set to |navigation id|, and the <code>url</code> field set to the
-   result of the [=URL serializer=] given |url|.
+1. Return a [=map=] matching the <code>browsingContext.NavigationInfo</code>
+   production, with the <code>context</code> field set to |context id|, the
+   <code>navigation</code> field set to |navigation id|, the
+   <code>timestamp</code> field set to |timestamp|, and the <code>url</code>
+   field set to the result of the [=URL serializer=] given |url|.
 
 </div>