Re-land "Replace requirePageReconstruction with setCustomUserAgent"

ios/web/web_view_creation_util.mm

 // Copyright 2014 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/web/public/web_view_creation_util.h"
 
 #include "base/logging.h"
+#include "ios/web/public/user_agent.h"
 #import "ios/web/web_state/ui/wk_web_view_configuration_provider.h"
 #import "ios/web/web_state/web_view_internal_creation_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace web {
 
 WKWebView* BuildWKWebView(CGRect frame, BrowserState* browser_state) {
   return BuildWKWebViewWithCustomContextMenu(frame, browser_state, nil);
 }
 
 WKWebView* BuildWKWebViewWithCustomContextMenu(
     CGRect frame,
     BrowserState* browser_state,
     id<CRWContextMenuDelegate> context_menu_delegate) {
   DCHECK(browser_state);
 
   WKWebViewConfigurationProvider& config_provider =
       WKWebViewConfigurationProvider::FromBrowserState(browser_state);
   return BuildWKWebView(frame, config_provider.GetWebViewConfiguration(),
-                        browser_state, NO, context_menu_delegate);
+                        browser_state, UserAgentType::MOBILE,
+                        context_menu_delegate);
 }
 
 }  // namespace web