Only create one downloads tab per window. If there is already a Downloads...

chrome/browser/external_tab_container.cc

 // Copyright (c) 2006-2008 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/external_tab_container.h"
 
 #include "base/logging.h"
 #include "base/win_util.h"
 #include "chrome/browser/automation/automation_provider.h"
 #include "chrome/browser/profile.h"
@@ skipping 173 matching lines @@
   return 0;
 }
 
 void ExternalTabContainer::OpenURLFromTab(TabContents* source,
                            const GURL& url,
                            const GURL& referrer,
                            WindowOpenDisposition disposition,
                            PageTransition::Type transition) {
   switch (disposition) {
     case CURRENT_TAB:
+    case SINGLETON_TAB:
     case NEW_FOREGROUND_TAB:
     case NEW_BACKGROUND_TAB:
     case NEW_WINDOW:
       if (automation_) {
         automation_->Send(new AutomationMsg_OpenURL(0, url, disposition));
       }
       break;
     default:
       break;
    }
@@ skipping 213 matching lines @@
   if (!::IsWindow(parent_window)) {
     return NULL;
   }
   if (!IsExternalTabContainer(parent_window)) {
     return NULL;
   }
   ExternalTabContainer* container = reinterpret_cast<ExternalTabContainer*>(
       GetProp(parent_window, kWindowObjectKey));
   return container;
 }