Adds NavigationManager util functions to ios/chrome/browser/web/

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 199 matching lines @@
       use_desktop_user_agent =
           last_non_native_item &&
           last_non_native_item->GetUserAgentType() == UserAgentType::DESKTOP;
     }
     if (use_desktop_user_agent)
       pending_item->SetUserAgentType(UserAgentType::DESKTOP);
   }
   override_desktop_user_agent_for_next_pending_item_ = false;
 }
 
-NavigationItem* NavigationManagerImpl::GetLastUserItem() const {
-  return [session_controller_ lastUserItem];
-}
-
 NavigationItemList NavigationManagerImpl::GetItems() const {
   return CreateNavigationItemList([session_controller_ items]);
 }
 
 BrowserState* NavigationManagerImpl::GetBrowserState() const {
   return browser_state_;
 }
 
 WebState* NavigationManagerImpl::GetWebState() const {
   return delegate_->GetWebState();
@@ skipping 233 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