Referrer Policy Demo (no-referrer-when-downgrade)

https://labs.w0s.jp/http/referrer-policy/no-referrer-when-downgrade_meta/ → https://whatsmyreferer.com/
`referrerpolicy` attribute	Referer Value
`(none)`	https://labs.w0s.jp/http/referrer-policy/no-referrer-when-downgrade_meta/
`referrerpolicy=""`	https://labs.w0s.jp/http/referrer-policy/no-referrer-when-downgrade_meta/
`referrerpolicy="no-referrer"`	(not be sent)
`referrerpolicy="no-referrer-when-downgrade"` (default)	https://labs.w0s.jp/http/referrer-policy/no-referrer-when-downgrade_meta/
`referrerpolicy="same-origin"`	(not be sent)
`referrerpolicy="origin"`	https://labs.w0s.jp/
`referrerpolicy="strict-origin"`	https://labs.w0s.jp/
`referrerpolicy="origin-when-cross-origin"`	https://labs.w0s.jp/
`referrerpolicy="strict-origin-when-cross-origin"` (Chrome 85+ default)	https://labs.w0s.jp/
`referrerpolicy="unsafe-url"`	https://labs.w0s.jp/http/referrer-policy/no-referrer-when-downgrade_meta/