(Set)IsOverridingUserAgent should be called on VisibleItem

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 402 matching lines @@
     // Result may be out of bounds, so stop trying to skip redirect items and
     // simply add the remainder.
     result += offset;
     if (result < 0 /* overflow */)
       result = INT_MAX;
   }
 
   return result;
 }
 
+bool NavigationManagerImpl::GetUseDesktopUserAgent() const {
+  return GetVisibleItem() && GetVisibleItem()->IsOverridingUserAgent();
+}
+
 void NavigationManagerImpl::OverrideDesktopUserAgentForNextPendingItem() {
   if (GetPendingItem())
     GetPendingItem()->SetIsOverridingUserAgent(true);
   else
     override_desktop_user_agent_for_next_pending_item_ = true;
 }
 
 bool NavigationManagerImpl::IsRedirectItemAtIndex(int index) const {
   DCHECK_GT(index, 0);
   DCHECK_LT(index, GetItemCount());
   ui::PageTransition transition = GetItemAtIndex(index)->GetTransitionType();
   return transition & ui::PAGE_TRANSITION_IS_REDIRECT_MASK;
 }
 
 }  // namespace web