The underlying reason behind the cookie's change. If a cookie was inserted,
or removed via an explicit call to "chrome.cookies.remove", "cause" will be
"explicit". If a cookie was automatically removed due to expiry, "cause"
will be "expired". If a cookie was removed due to being overwritten with an
already-expired expiration date, "cause" will be set to "expired_overwrite".
If a cookie was automatically removed due to garbage collection, "cause"
will be "evicted". If a cookie was automatically removed due to a "set"
call that overwrote it, "cause" will be "overwrite". Plan your response
accordingly.
A cookie's 'SameSite' state
(https://tools.ietf.org/html/draft-west-first-party-cookies).
'no_restriction' corresponds to a cookie set with 'SameSite=None', 'lax' to
'SameSite=Lax', and 'strict' to 'SameSite=Strict'. 'unspecified' corresponds
to a cookie set without the SameSite attribute.
