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

ios/web/navigation/navigation_manager_impl.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/navigation/navigation_manager_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 152 matching lines @@
 }
 
 void NavigationManagerImpl::LoadURL(const GURL& url,
                                     const web::Referrer& referrer,
                                     ui::PageTransition type) {
   WebState::OpenURLParams params(url, referrer,
                                  WindowOpenDisposition::CURRENT_TAB, type, NO);
   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,
     ui::PageTransition navigation_type,
     NavigationInitiationType initiation_type,
     UserAgentOverrideOption user_agent_override_option) {
   [session_controller_ addPendingItem:url
                              referrer:referrer
                            transition:navigation_type
                        initiationType:initiation_type];
@@ skipping 275 matching lines @@
   const ScopedNavigationItemImplList& items = [session_controller_ items];
   while (index >= 0) {
     NavigationItem* item = items[index--].get();
     if (!client->IsAppSpecificURL(item->GetVirtualURL()))
       return item;
   }
   return nullptr;
 }
 
 }  // namespace web