[css-anchor-1] Preserve the previously used fallback position when all fallbacks fail

[chromium-helper]

CSSWG added the following resolution(s):

• RESOLVED: Modulo timing details and things that should cause us to forget, the last successful fallback position is used when all options fail
• RESOLVED: If there's no previously successful fallback, we'll use the base styles with no fallback rules applied

in w3c/csswg-drafts#8200 (comment)

[chromium-helper]

I have filed issues.chromium.org/329302050

That is all that can be done here, closing issue.