Convert //ios/web_view/internal to ARC.

ios/web_view/internal/criwv_web_main_delegate.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_view/internal/criwv_web_main_delegate.h"
 
 #include "base/memory/ptr_util.h"
 #import "ios/web_view/internal/criwv_web_client.h"
 #import "ios/web_view/public/criwv_delegate.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace ios_web_view {
 
 CRIWVWebMainDelegate::CRIWVWebMainDelegate(id<CRIWVDelegate> delegate)
     : delegate_(delegate) {}
 
 CRIWVWebMainDelegate::~CRIWVWebMainDelegate() {}
 
 void CRIWVWebMainDelegate::BasicStartupComplete() {
   web_client_ = base::MakeUnique<CRIWVWebClient>(delegate_);
   web::SetWebClient(web_client_.get());
 }
 
 }  // namespace ios_web_view