Make containing block of position:fixed dialog children the viewport.
Created attachment 463536 [details] Patch
This patch modifies the imported WPT tests. Please ensure that any changes on the tests (not coming from a WPT import) are exported to WPT. Please see https://trac.webkit.org/wiki/WPTExportProcess
Committed 256724@main (c13598861f40): <https://commits.webkit.org/256724@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 463536 [details].
<rdar://problem/102407190>