[ObjC ARC] Converts ios/chrome/browser/ui/dialogs:dialogs_internal to ARC.

ios/chrome/browser/ui/dialogs/java_script_dialog_presenter_impl.mm

 // Copyright 2016 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.
 
 #include "ios/chrome/browser/ui/dialogs/java_script_dialog_presenter_impl.h"
 
 #import "ios/chrome/browser/ui/dialogs/dialog_presenter.h"
 #import "ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 JavaScriptDialogPresenterImpl::JavaScriptDialogPresenterImpl(
     DialogPresenter* dialogPresenter)
-    : dialog_presenter_([dialogPresenter retain]) {}
+    : dialog_presenter_(dialogPresenter) {}
 
 JavaScriptDialogPresenterImpl::~JavaScriptDialogPresenterImpl() {}
 
 void JavaScriptDialogPresenterImpl::RunJavaScriptDialog(
     web::WebState* web_state,
     const GURL& origin_url,
     web::JavaScriptDialogType dialog_type,
     NSString* message_text,
     NSString* default_prompt_text,
     const web::DialogClosedCallback& callback) {
@@ skipping 43 matching lines @@
       break;
     }
     default:
       break;
   }
 }
 
 void JavaScriptDialogPresenterImpl::CancelDialogs(web::WebState* web_state) {
   [dialog_presenter_ cancelDialogForWebState:web_state];
 }