Re-land "Replace requirePageReconstruction with setCustomUserAgent"

ios/web/web_state/web_view_internal_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/web_state/web_view_internal_creation_util.h"
 
 #import <objc/runtime.h>
 
 #include "base/logging.h"
 #import "base/mac/scoped_nsobject.h"
@@ skipping 18 matching lines @@
       WKWebViewConfigurationProvider::FromBrowserState(browser_state);
   DCHECK_EQ([config_provider.GetWebViewConfiguration() processPool],
             [configuration processPool]);
 }
 
 }  // namespace
 
 WKWebView* BuildWKWebView(CGRect frame,
                           WKWebViewConfiguration* configuration,
                           BrowserState* browser_state,
-                          BOOL use_desktop_user_agent,
+                          UserAgentType user_agent_type,
                           id<CRWContextMenuDelegate> context_menu_delegate) {
   VerifyWKWebViewCreationPreConditions(browser_state, configuration);
 
   GetWebClient()->PreWebViewCreation();
   WKWebView* web_view =
       [[WKWebView alloc] initWithFrame:frame configuration:configuration];
 
-  // Set the user agent.
-  UserAgentType user_agent_type =
-      use_desktop_user_agent ? UserAgentType::DESKTOP : UserAgentType::MOBILE;
-  web_view.customUserAgent = base::SysUTF8ToNSString(
-      web::GetWebClient()->GetUserAgent(user_agent_type));
+  if (user_agent_type != web::UserAgentType::NONE) {
+    web_view.customUserAgent = base::SysUTF8ToNSString(
+        web::GetWebClient()->GetUserAgent(user_agent_type));
+  }
 
   // By default the web view uses a very sluggish scroll speed. Set it to a more
   // reasonable value.
   web_view.scrollView.decelerationRate = UIScrollViewDecelerationRateNormal;
 
   // Starting in iOS10, |allowsLinkPreview| defaults to YES.  This should be
   // disabled since the default implementation will open the link in Safari.
   // TODO(crbug.com/622746): Remove once web// link preview implementation is
   // created.
   web_view.allowsLinkPreview = NO;
 
   if (context_menu_delegate) {
     base::scoped_nsobject<CRWContextMenuController> context_menu_controller(
         [[CRWContextMenuController alloc]
                initWithWebView:web_view
             injectionEvaluator:nil
                       delegate:context_menu_delegate]);
     objc_setAssociatedObject(web_view, context_menu_controller.get(),
                              context_menu_controller.get(),
                              OBJC_ASSOCIATION_RETAIN_NONATOMIC);
   }
 
   return [web_view autorelease];
 }
 
 WKWebView* BuildWKWebView(CGRect frame,
                           WKWebViewConfiguration* configuration,
                           BrowserState* browser_state,
-                          BOOL use_desktop_user_agent) {
-  return BuildWKWebView(frame, configuration, browser_state,
-                        use_desktop_user_agent, nil);
+                          UserAgentType user_agent_type) {
+  return BuildWKWebView(frame, configuration, browser_state, user_agent_type,
+                        nil);
 }
 
 WKWebView* BuildWKWebView(CGRect frame,
                           WKWebViewConfiguration* configuration,
                           BrowserState* browser_state) {
-  BOOL use_desktop_user_agent = NO;
   return BuildWKWebView(frame, configuration, browser_state,
-                        use_desktop_user_agent);
+                        UserAgentType::MOBILE);
 }
 
 }  // namespace web