[Mac] Break stale controller refs in infobar close.

chrome/browser/ui/cocoa/translate/translate_infobar_base.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_TRANSLATE_INFOBAR_BASE_H_
 #define CHROME_BROWSER_UI_COCOA_TRANSLATE_INFOBAR_BASE_H_
 #pragma once
 
 #import <Cocoa/Cocoa.h>
 #import "chrome/browser/ui/cocoa/infobars/infobar_controller.h"
@@ skipping 58 matching lines @@
   bool swappedLanguagePlaceholders_;
 
   // Space between controls in pixels - read from the NIB.
   CGFloat spaceBetweenControls_;
 
   scoped_ptr<LanguagesMenuModel> originalLanguageMenuModel_;
   scoped_ptr<LanguagesMenuModel> targetLanguageMenuModel_;
   scoped_ptr<OptionsMenuModel> optionsMenuModel_;
 }
 
-// Returns the delegate as a TranslateInfoBarDelegate.
+// Returns the delegate as a TranslateInfoBarDelegate.  The return
+// value can be NULL if the infobar is closing.
 - (TranslateInfoBarDelegate*)delegate;
 
 // Called when the "Show Original" button is pressed.
 - (IBAction)showOriginal:(id)sender;
 
 @end
 
 @interface TranslateInfoBarControllerBase (ProtectedAPI)
 
 // Resizes or hides the options button based on how much space is available
@@ skipping 64 matching lines @@
 - (NSMenu*)optionsMenu;
 
 // Returns |translateMessageButton_|, see declaration of member
 // variable for a full description.
 - (NSButton*)translateMessageButton;
 
 @end // TranslateInfoBarControllerBase (TestingAPI)
 
 
 #endif // CHROME_BROWSER_UI_COCOA_TRANSLATE_INFOBAR_BASE_H_