According to the spec, canceling lazy loading should happen before navigating to a fragment. If we cancel lazy loading in DoURILoad, we won't cancel for same document navigation. To my knowledge, this hasn't been an issue. But with sync-about-blank, this would break wpt iframe-loading-lazy-nav-link-click-fragment.html. Differential Revision: https://phabricator.services.mozilla.com/D234665