[iOS] Fix trust condition for file scheme

This CL makes sure that the last committed item is trusted when it
has a file scheme. I think this was the intend when the code was written
as the check for the about scheme is here twice.

Bug: 991608
Change-Id: I5b2f44351e8b73ccf3804c173db944d49557c477
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401022
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806088}

ios/web/navigation/wk_based_navigation_manager_impl.mm

@@ -469,7 +469,7 @@ bool WKBasedNavigationManagerImpl::CanTrustLastCommittedItem(
   if (web_view_url.SchemeIs(url::kAboutScheme) ||
       last_committed_url.SchemeIs(url::kAboutScheme) ||
       web_view_url.SchemeIs(url::kFileScheme) ||
-      last_committed_url.SchemeIs(url::kAboutScheme) ||
+      last_committed_url.SchemeIs(url::kFileScheme) ||
       web::GetWebClient()->IsAppSpecificURL(web_view_url) ||
       web::GetWebClient()->IsAppSpecificURL(last_committed_url)) {
     return true;