Use delegate protocols present in the 10.6 SDK

chrome/browser/app_modal_dialog_mac.mm

 // Copyright (c) 2009 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 "chrome/browser/app_modal_dialog.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "app/l10n_util_mac.h"
 #include "app/message_box_flags.h"
+#import "base/cocoa_protocols_mac.h"
 #include "base/sys_string_conversions.h"
 #include "grit/app_strings.h"
 #include "grit/generated_resources.h"
 
 // Helper object that receives the notification that the dialog/sheet is
 // going away. Is responsible for cleaning itself up.
-@interface AppModalDialogHelper : NSObject {
+@interface AppModalDialogHelper : NSObject<NSAlertDelegate> {
  @private
   NSAlert* alert_;
   NSTextField* textField_;  // WEAK; owned by alert_
 }
 
 - (NSAlert*)alert;
 - (NSTextField*)textField;
 - (void)alertDidEnd:(NSAlert *)alert
          returnCode:(int)returnCode
         contextInfo:(void*)contextInfo;
@@ skipping 116 matching lines @@
   return 0;
 }
 
 void AppModalDialog::AcceptWindow() {
   NOTIMPLEMENTED();
 }
 
 void AppModalDialog::CancelWindow() {
   NOTIMPLEMENTED();
 }