LibWeb: Use document's viewport when resolving lengths in media queries

Previously we would always use the window's viewport which was incorrect
if we were within an iframe.

This is likely applicable to all uses of
`Length::ResolutionContext::for_window`.

Libraries/LibWeb/CSS/MediaList.cpp

@@ -109,10 +109,10 @@ void MediaList::delete_medium(StringView medium)
     // FIXME: If nothing was removed, then throw a NotFoundError exception.
 }
 
-bool MediaList::evaluate(HTML::Window const& window)
+bool MediaList::evaluate(DOM::Document const& document)
 {
     for (auto& media : m_media)
-        media->evaluate(window);
+        media->evaluate(document);
 
     return matches();
 }