Also treat new background tabs as pop-ups.

chrome/browser/ui/browser_tabstrip.cc

 // 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/browser_tabstrip.h"
 
 #include "base/command_line.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/blocked_content/blocked_content_tab_helper.h"
 #include "chrome/browser/ui/browser.h"
@@ skipping 52 matching lines @@
     // Handle blocking of tabs.
     if (source_blocked_content->all_contents_blocked()) {
       source_blocked_content->AddWebContents(
           new_contents, disposition, initial_pos, user_gesture);
       if (was_blocked)
         *was_blocked = true;
       return;
     }
 
     // Handle blocking of popups.
-    if ((disposition == NEW_POPUP || disposition == NEW_FOREGROUND_TAB) &&
-        !user_gesture &&
+    if ((disposition == NEW_POPUP || disposition == NEW_FOREGROUND_TAB ||
+         disposition == NEW_BACKGROUND_TAB) && !user_gesture &&
         !CommandLine::ForCurrentProcess()->HasSwitch(
             switches::kDisablePopupBlocking)) {
       // Unrequested popups from normal pages are constrained unless they're in
       // the white list.  The popup owner will handle checking this.
       source_blocked_content->AddPopup(
           new_contents, disposition, initial_pos, user_gesture);
       if (was_blocked)
         *was_blocked = true;
       return;
     }
@@ skipping 19 matching lines @@
     return;
   }
 
   browser->tab_strip_model()->CloseWebContentsAt(
       index,
       add_to_history ? TabStripModel::CLOSE_CREATE_HISTORICAL_TAB
                      : TabStripModel::CLOSE_NONE);
 }
 
 }  // namespace chrome