[iOS] Use the request_url for SSLBlockingPage

This CL updates the way the SSLBlockingPage are detecting the page
for which an exception is being added by using the URL passed in the
initialisation rather than the URL of the page sending the JavaScript
command, as it is a file:// URL when using the new error page workflow.

Bug: 1139303
Change-Id: Ia27a656ecdca52c16503b3c5d1b9cbf594543b47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2509518Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824820}

ios/chrome/browser/ssl/ios_ssl_blocking_page.mm

@@ -165,7 +165,7 @@ void IOSSSLBlockingPage::HandleScriptCommand(
   // the page to re-initiate the original navigation.
   if (command_num == security_interstitials::CMD_PROCEED) {
     web_state_->GetSessionCertificatePolicyCache()->RegisterAllowedCertificate(
-        ssl_info_.cert, origin_url.host(), ssl_info_.cert_status);
+        ssl_info_.cert, request_url().host(), ssl_info_.cert_status);
     web_state_->GetNavigationManager()->Reload(web::ReloadType::NORMAL,
                                                /*check_for_repost=*/true);
     return;