[iOS] Refactoring web CRWSessionController user agent code.

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 b246e7e17e03c15ebaf0ace9fb3799b016ecf84a..0eab696684f141e3cf1a2ca8043012c5222e50be 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -68,7 +68,10 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
 }
 
 NavigationManagerImpl::NavigationManagerImpl()
-    : delegate_(nullptr), browser_state_(nullptr), facade_delegate_(nullptr) {}
+    : override_desktop_user_agent_for_next_pending_item_(false),
+      delegate_(nullptr),
+      browser_state_(nullptr),
+      facade_delegate_(nullptr) {}
 
 NavigationManagerImpl::~NavigationManagerImpl() {
   // The facade layer should be deleted before this object.
@@ -173,6 +176,25 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
   delegate_->GetWebState()->OpenURL(params);
 }
 
+void NavigationManagerImpl::AddPendingItem(const GURL& url,
+                                           const web::Referrer& referrer,
+                                           ui::PageTransition navigation_type,
+                                           ItemInitiationType initiation_type) {
+  bool renderer_initiated =
+      initiation_type == ItemInitiationType::RENDERER_INITIATED;
+  [session_controller_ addPendingItem:url
+                             referrer:referrer
+                           transition:navigation_type
+                    rendererInitiated:renderer_initiated];
+
+  bool use_desktop_user_agent =
+      override_desktop_user_agent_for_next_pending_item_ ||
+      (GetLastCommittedItem() &&
+       GetLastCommittedItem()->IsOverridingUserAgent());
+  GetPendingItem()->SetIsOverridingUserAgent(use_desktop_user_agent);
+  override_desktop_user_agent_for_next_pending_item_ = false;
+}
+
 NavigationItem* NavigationManagerImpl::GetLastUserItem() const {
   CRWSessionEntry* entry = [session_controller_ lastUserEntry];
   return [entry navigationItem];
@@ -396,6 +418,13 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
   return result;
 }
 
+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());