[css-view-transitions-2] Skip cross-document view-transitions when hidden or not-yet-revealed (w3c#9948)

* [css-view-transitions-2] Skip cross-document view-transitions when hidden or not-yet-revealed

Closes w3c#9822
See also w3c#9543

* Add dfn

Author: noamr

css-view-transitions-2/Overview.bs

@@ -49,6 +49,7 @@ spec:html
 	text: run the animation frame callbacks; type: dfn;
 	text: unload; type: dfn;
 	text: pagereveal; type: dfn; for: Window;
+	text: has been revealed; type: dfn;
 spec:infra; type:dfn; text:list
 </pre>
 
@@ -613,6 +614,9 @@ Prepend this to the [=Perform pending transition operations=] algorithm given a
 	<div algorithm>
 		To get the <dfn>resolve @view-transition rule</dfn> for a {{Document}} |document|:
 
+		1. If |document|'s [=Document/visibility state=] is "<code>hidden</code>",
+			then return "<code>skip transition</code>".
+
 		1. Let |matchingRule| be the last ''@view-transition'' rule in |document|.
 
 		1. If |matchingRule| is not found, then return "<code>skip transition</code>".
@@ -655,6 +659,8 @@ Prepend this to the [=Perform pending transition operations=] algorithm given a
 
 		1. [=Assert=]: These steps are running as part of a [=task=] queued on |oldDocument|.
 
+		1. If |oldDocument|'s [=has been revealed=] is false, then return null.
+
 		1. Let |resolvedRule| be the result of [=Resolve @view-transition rule|resolving the @view-transition rule=] for |oldDocument|.
 
 		1. If |resolvedRule| is "<code>skip transition</code>", then return null.