Reland of Set user agent type of transient item the same as pending item

ios/web/navigation/navigation_manager_impl.mm

Index: ios/web/navigation/navigation_manager_impl.mm
diff --git a/ios/web/navigation/navigation_manager_impl.mm b/ios/web/navigation/navigation_manager_impl.mm
index da2ae03a14d715f438312e472af75142eecc141b..54f69e5f33a0a7cb8a25256292935d1a0832580d 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -170,6 +170,19 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
   delegate_->GetWebState()->OpenURL(params);
 }
 
+void NavigationManagerImpl::AddTransientItem(const GURL& url) {
+  [session_controller_ addTransientItemWithURL:url];
+
+  // TODO(crbug.com/676129): Transient item is only supposed to be added for
+  // pending non-app-specific loads, but pending item can be null because of the
+  // bug. The workaround should be removed once the bug is fixed.
+  NavigationItem* item = GetPendingItem();
+  if (!item)
+    item = GetLastCommittedNonAppSpecificItem();
+  DCHECK(item->GetUserAgentType() != UserAgentType::NONE);
+  GetTransientItem()->SetUserAgentType(item->GetUserAgentType());
+}
+
 void NavigationManagerImpl::AddPendingItem(
     const GURL& url,
     const web::Referrer& referrer,