Do not show the install prompt for themes.

chrome/common/chrome_notification_types.h

 // 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.
 
 #ifndef CHROME_COMMON_CHROME_NOTIFICATION_TYPES_H_
 #define CHROME_COMMON_CHROME_NOTIFICATION_TYPES_H_
 #pragma once
 
 #include "content/public/browser/notification_types.h"
 
@@ skipping 157 matching lines @@
   // Sent when the bookmark bubble hides. The source is the profile, the
   // details unused.
   NOTIFICATION_BOOKMARK_BUBBLE_HIDDEN,
 
   // This notification is sent when the result of a find-in-page search is
   // available with the browser process. The source is a Source<WebContents>.
   // Details encompass a FindNotificationDetail object that tells whether the
   // match was found or not found.
   NOTIFICATION_FIND_RESULT_AVAILABLE,
 
-  // Sent just before the installation confirm dialog is shown. The source
-  // is the ExtensionInstallUI, the details are NoDetails.
-  NOTIFICATION_EXTENSION_WILL_SHOW_CONFIRM_DIALOG,
-
   // BackgroundContents ------------------------------------------------------
 
   // A new background contents was opened by script. The source is the parent
   // profile and the details are BackgroundContentsOpenedDetails.
   NOTIFICATION_BACKGROUND_CONTENTS_OPENED,
 
   // The background contents navigated to a new location. The source is the
   // parent Profile, and the details are the BackgroundContents that was
   // navigated.
   NOTIFICATION_BACKGROUND_CONTENTS_NAVIGATED,
@@ skipping 898 matching lines @@
   // Currently only Content and Chrome define and use notifications.
   // Custom notifications not belonging to Content and Chrome should start
   // from here.
   NOTIFICATION_CHROME_END,
 };
 
 }  // namespace chrome
 
 
 #endif  // CHROME_COMMON_CHROME_NOTIFICATION_TYPES_H_