Fix crash when programatically closing media gallery dialog

chrome/browser/ui/cocoa/extensions/media_galleries_dialog_cocoa.mm

 // Copyright (c) 2012 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/ui/cocoa/extensions/media_galleries_dialog_cocoa.h"
 
 #include "base/sys_string_conversions.h"
 #include "chrome/browser/ui/tab_contents/tab_contents.h"
 #include "grit/generated_resources.h"
 #include "ui/base/l10n/l10n_util.h"
@@ skipping 116 matching lines @@
   switch (result) {
     case NSAlertFirstButtonReturn:
       accepted_ = true;
       if (window_)
         window_->CloseConstrainedWindow();
       break;
     case NSAlertSecondButtonReturn:
       if (window_)
         window_->CloseConstrainedWindow();
       break;
+    case NSRunStoppedResponse:
+      break;
     default:
       NOTREACHED();
       break;
   }
 }
 
 void MediaGalleriesDialogCocoa::UpdateGalleryCheckbox(
     NSButton* checkbox,
     const MediaGalleryPrefInfo* gallery,
     bool permitted) {
@@ skipping 51 matching lines @@
 
   UpdateGalleryCheckbox(checkbox, gallery, permitted);
   UpdateCheckboxContainerFrame();
   [alert_ layout];
 }
 
 void MediaGalleriesDialogCocoa::DeleteDelegate() {
   // As required by ConstrainedWindowMacDelegate, close the sheet if
   // it's still open.
   if (is_sheet_open())
-    [NSApp endSheet:sheet()];
+    [NSApp endSheet:[alert_ window]];
 
   controller_->DialogFinished(accepted_);
 }
 
 // static
 MediaGalleriesDialog* MediaGalleriesDialog::Create(
     MediaGalleriesDialogController* controller) {
   scoped_nsobject<MediaGalleriesCocoaController> cocoa_controller(
       [[MediaGalleriesCocoaController alloc] init]);
   return new MediaGalleriesDialogCocoa(controller, cocoa_controller);
 }
 
 }  // namespace chrome