Revert of [ObjC ARC] Converts ios/chrome/browser/ui:ui to ARC.

ios/chrome/browser/ui/show_mail_composer_util.mm

Index: ios/chrome/browser/ui/show_mail_composer_util.mm
diff --git a/ios/chrome/browser/ui/show_mail_composer_util.mm b/ios/chrome/browser/ui/show_mail_composer_util.mm
index b1f6fde7d393ac6b6d7365799d1e37958916a47e..2d9624c56b1506cda08b68cc272a715c022e2aed 100644
--- a/ios/chrome/browser/ui/show_mail_composer_util.mm
+++ b/ios/chrome/browser/ui/show_mail_composer_util.mm
@@ -7,13 +7,10 @@
 #include <UIKit/UIKit.h>
 
 #include "base/logging.h"
+#include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #include "ios/chrome/browser/ui/commands/UIKit+ChromeExecuteCommand.h"
 #include "ios/chrome/browser/ui/commands/show_mail_composer_command.h"
-
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif
 
 void ShowMailComposer(const base::string16& to_recipient,
                       const base::string16& subject,
@@ -22,12 +19,13 @@
                       const base::FilePath& text_file_to_attach,
                       int email_not_configured_alert_title_id,
                       int email_not_configured_alert_message_id) {
-  ShowMailComposerCommand* command = [[ShowMailComposerCommand alloc]
+  base::scoped_nsobject<ShowMailComposerCommand>
+  command([[ShowMailComposerCommand alloc]
                    initWithToRecipient:base::SysUTF16ToNSString(to_recipient)
                                subject:base::SysUTF16ToNSString(subject)
                                   body:base::SysUTF16ToNSString(body)
         emailNotConfiguredAlertTitleId:email_not_configured_alert_title_id
-      emailNotConfiguredAlertMessageId:email_not_configured_alert_message_id];
+      emailNotConfiguredAlertMessageId:email_not_configured_alert_message_id]);
   [command setTextFileToAttach:text_file_to_attach];
   UIWindow* main_window = [[UIApplication sharedApplication] keyWindow];
   DCHECK(main_window);