||Permission delegate handler provides a policy of how top-level can
delegate permission to embedded iframes.
This class includes a mechanism to delegate permission using feature
policy. Feature policy will assure that only cross-origin iframes which
have been explicitly granted access will have the opportunity to request
For example if an iframe has not been granted access to geolocation by
Feature Policy, geolocation request from the iframe will be automatically
denied. if the top-level origin already has access to geolocation and the
iframe has been granted access to geolocation by Feature Policy, the iframe
will also have access to geolocation. If the top-level frame did not have
access to geolocation, and the iframe has been granted access to geolocation
by Feature Policy, a request from the cross-origin iframe would trigger a
prompt using of the top-level origin.
||PermissionKey is the key used by PermissionHashKey hash table.