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

ios/chrome/browser/tabs/tab.mm

 // Copyright 2012 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/chrome/browser/tabs/tab.h"
 
 #import <CoreLocation/CoreLocation.h>
 #import <UIKit/UIKit.h>
 
 #include <utility>
@@ skipping 1461 matching lines @@
 
   [self.readerModeController exitReaderMode];
 }
 
 #pragma mark -
 
 - (BOOL)usesDesktopUserAgent {
   if (!self.navigationManager)
     return NO;
 
-  web::NavigationItem* visibleItem = self.navigationManager->GetVisibleItem();
-  return visibleItem &&
-         visibleItem->GetUserAgentType() == web::UserAgentType::DESKTOP;
+  // TODO(crbug.com/707081): Clean this up once the bug is fixed.
+  web::NavigationItem* item = self.navigationManager->GetTransientItem();
+  if (!item)
+    item = self.navigationManager->GetPendingItem();
+  if (!item)
+    item = self.navigationManager->GetLastCommittedItem();
+
+  return item && item->GetUserAgentType() == web::UserAgentType::DESKTOP;
 }
 
 - (void)enableDesktopUserAgent {
   DCHECK_EQ(self.usesDesktopUserAgent, NO);
   DCHECK([self navigationManager]);
   [self navigationManager]->OverrideDesktopUserAgentForNextPendingItem();
 }
 
 - (void)reloadForDesktopUserAgent {
   // This removes the web view, which will be recreated at the end of this.
@@ skipping 592 matching lines @@
 
 - (TabModel*)parentTabModel {
   return parentTabModel_;
 }
 
 - (FormInputAccessoryViewController*)inputAccessoryViewController {
   return inputAccessoryViewController_.get();
 }
 
 @end