add DCHECK that a server redirect pending item should never be added.

ios/web/navigation/navigation_manager_impl_unittest.mm

Index: ios/web/navigation/navigation_manager_impl_unittest.mm
diff --git a/ios/web/navigation/navigation_manager_impl_unittest.mm b/ios/web/navigation/navigation_manager_impl_unittest.mm
index 9bc5a3ac7834038a92750ab2d15cec013df52c00..7bac7552ab46256554b5a441339fd7f0aba2b974 100644
--- a/ios/web/navigation/navigation_manager_impl_unittest.mm
+++ b/ios/web/navigation/navigation_manager_impl_unittest.mm
@@ -254,7 +254,7 @@ void OnNavigationItemCommitted(const LoadCommittedDetails&) override {}
   [session_controller() commitPendingItem];
   navigation_manager()->AddPendingItem(
       GURL("http://www.url.com/redirect"), Referrer(),
-      ui::PAGE_TRANSITION_IS_REDIRECT_MASK,
+      ui::PAGE_TRANSITION_CLIENT_REDIRECT,
       web::NavigationInitiationType::USER_INITIATED);
   [session_controller() commitPendingItem];
   navigation_manager()->AddPendingItem(
@@ -267,7 +267,7 @@ void OnNavigationItemCommitted(const LoadCommittedDetails&) override {}
   [session_controller() commitPendingItem];
   navigation_manager()->AddPendingItem(
       GURL("http://www.url.com/redirect"), Referrer(),
-      ui::PAGE_TRANSITION_IS_REDIRECT_MASK,
+      ui::PAGE_TRANSITION_CLIENT_REDIRECT,
       web::NavigationInitiationType::USER_INITIATED);
   [session_controller() commitPendingItem];
   ASSERT_EQ(5, navigation_manager()->GetItemCount());