couldCanonicalize method
Without accessing the filesystem, returns whether or not passing url to
canonicalize could possibly return canonicalUrl.
This is expected to be very efficient, and subclasses are allowed to
return false positives if it would be inefficient to determine whether
url would actually resolve to canonicalUrl. Subclasses are not allowed
to return false negatives.
Implementation
bool couldCanonicalize(Uri url, Uri canonicalUrl) => true;