implement user agent override option.

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 604 matching lines @@
                              referrer:(const web::Referrer&)referrer
                            transition:(ui::PageTransition)transition
                              provider:(id<CRWNativeContentProvider>)provider
                                opener:(Tab*)opener
                      desktopUserAgent:(BOOL)desktopUserAgent
                         configuration:(void (^)(Tab*))configuration {
   Tab* tab = [[[Tab alloc] initWithBrowserState:browserState
                                          opener:opener
                                     openedByDOM:NO
                                           model:nil] autorelease];
-  if (desktopUserAgent)
-    [tab enableDesktopUserAgent];
   [[tab webController] setNativeProvider:provider];
   [[tab webController] setWebUsageEnabled:YES];
 
   if (configuration)
     configuration(tab);
 
   web::NavigationManager::WebLoadParams params(URL);
   params.transition_type = transition;
   params.referrer = referrer;
+  if (desktopUserAgent) {
+    params.user_agent_override_option =
+        web::NavigationManager::UserAgentOverrideOption::DESKTOP;
+  }
+
   [[tab webController] loadWithParams:params];
 
   return tab;
 }
 
 - (void)dealloc {
   DCHECK([NSThread isMainThread]);
   // Note that -[CRWWebController close] has already been called, so nothing
   // significant should be done with it in this method.
   DCHECK_NE(self.webController.delegate, self);
@@ skipping 831 matching lines @@
 
 - (BOOL)usesDesktopUserAgent {
   if (!self.navigationManager)
     return NO;
 
   web::NavigationItem* visibleItem = self.navigationManager->GetVisibleItem();
   return visibleItem &&
          visibleItem->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.
   [self.webController requirePageReconstruction];
 
   // TODO(crbug.com/228171): A hack in session_controller -addPendingItem
   // discusses making tab responsible for distinguishing history stack
   // navigation from new navigations.
   web::NavigationManager* navigationManager = [self navigationManager];
   DCHECK(navigationManager);
   web::NavigationItem* lastNonRedirectedItem =
       GetLastNonRedirectedItem(navigationManager);
   if (!lastNonRedirectedItem)
     return;
 
   // |reloadURL| will be empty if a page was open by DOM.
   GURL reloadURL(lastNonRedirectedItem->GetOriginalRequestURL());
   if (reloadURL.is_empty()) {
     DCHECK(self.webState && self.webState->HasOpener());
     reloadURL = lastNonRedirectedItem->GetVirtualURL();
   }
 
   web::NavigationManager::WebLoadParams params(reloadURL);
   params.referrer = lastNonRedirectedItem->GetReferrer();
   // A new navigation is needed here for reloading with desktop User-Agent.
+  params.user_agent_override_option =
+      web::NavigationManager::UserAgentOverrideOption::DESKTOP;
   params.transition_type =
       ui::PageTransitionFromInt(ui::PAGE_TRANSITION_FORM_SUBMIT);
   navigationManager->LoadURLWithParams(params);
 }
 
 - (id<SnapshotOverlayProvider>)snapshotOverlayProvider {
   return snapshotOverlayProvider_.get();
 }
 
 - (void)setSnapshotOverlayProvider:
@@ skipping 560 matching lines @@
 
 - (TabModel*)parentTabModel {
   return parentTabModel_;
 }
 
 - (FormInputAccessoryViewController*)inputAccessoryViewController {
   return inputAccessoryViewController_.get();
 }
 
 @end