Stumbled on this in a code review:

void CookieStoreIOS::DeleteCanonicalCookieAsync(const CanonicalCookie& cookie,
   ....

  // This relies on the fact cookies are given unique creation dates.
  CookieFilterFunction filter = base::Bind(
      IsCookieCreatedBetween, cookie.CreationDate(), cookie.CreationDate());
  DeleteCookiesWithFilterAsync(std::move(filter), std::move(callback));
}

CookieMonster has been moving away from having unique creation dates, so this might no longer 
work correctly now, or stop working soon. I haven't looked at iOS code yet[1], though, so this may be wrong,
but seems worth due diligence.

[1] This bit came up in a code review.