implement user agent override option.

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index b959f8a6b18874a996791ea2fe4cfbfbd57cb58e..62ff91e23ebe5f606e1e89373967bc5e6d8fa0a7 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -1493,7 +1493,8 @@ - (void)registerLoadRequest:(const GURL&)requestURL
     // A new session history entry needs to be created.
     self.navigationManagerImpl->AddPendingItem(
         requestURL, referrer, transition,
-        web::NavigationInitiationType::RENDERER_INITIATED);
+        web::NavigationInitiationType::RENDERER_INITIATED,
+        web::NavigationManager::UserAgentOverrideOption::INHERIT);
   }
   _webStateImpl->SetIsLoading(true);
   _webStateImpl->OnProvisionalNavigationStarted(requestURL);
@@ -1819,7 +1820,8 @@ - (void)loadWithParams:(const NavigationManager::WebLoadParams&)originalParams {
           ? web::NavigationInitiationType::RENDERER_INITIATED
           : web::NavigationInitiationType::USER_INITIATED;
   self.navigationManagerImpl->AddPendingItem(
-      navUrl, params.referrer, transition, navigationInitiationType);
+      navUrl, params.referrer, transition, navigationInitiationType,
+      params.user_agent_override_option);
 
   web::NavigationItemImpl* addedItem = self.currentNavItem;
   DCHECK(addedItem);