implement user agent override option.

ios/chrome/browser/ui/browser_view_controller.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/ui/browser_view_controller.h"
 
 #import <AssetsLibrary/AssetsLibrary.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 #import <PassKit/PassKit.h>
 #import <Photos/Photos.h>
@@ skipping 4204 matching lines @@
 
 - (void)showHelpPage {
   GURL helpUrl(l10n_util::GetStringUTF16(IDS_IOS_TOOLS_MENU_HELP_URL));
   [self webPageOrderedOpen:helpUrl
                   referrer:web::Referrer()
               inBackground:NO
                   appendTo:kCurrentTab];
 }
 
 - (void)enableDesktopUserAgent {
-  [[_model currentTab] enableDesktopUserAgent];
   [[_model currentTab] reloadForDesktopUserAgent];
 }
 
 // TODO(crbug.com/692303): Implement the actual functionality of
 // "Request Mobile Site", and also refactoring the user agent related function
 // names to improve readability.
 - (void)enableMobileUserAgent {
 }
 
 - (void)resetAllWebViews {
@@ skipping 890 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end