Show singleton tab instead of opening multiple help tabs.

chrome/browser/ui/browser.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_BROWSER_H_
 #define CHROME_BROWSER_UI_BROWSER_H_
 #pragma once
 
 #include <map>
 #include <set>
@@ skipping 560 matching lines @@
   // Shows the Content Settings page for a given content type.
   void ShowContentSettingsPage(ContentSettingsType content_type);
   void OpenClearBrowsingDataDialog();
   void OpenOptionsDialog();
   void OpenPasswordManager();
   void OpenSyncMyBookmarksDialog();
   void OpenImportSettingsDialog();
   void OpenInstantConfirmDialog();
   void OpenAboutChromeDialog();
   void OpenUpdateChromeDialog();
-  void OpenHelpTab();
+  void ShowHelpTab();
   // Used by the "Get themes" link in the options dialog.
   void OpenThemeGalleryTabAndActivate();
   void OpenAutofillHelpTabAndActivate();
   void OpenPrivacyDashboardTabAndActivate();
   void OpenSearchEngineOptionsDialog();
 #if defined(OS_CHROMEOS)
   void OpenFileManager();
   void OpenSystemOptionsDialog();
   void OpenInternetOptionsDialog();
   void OpenLanguageOptionsDialog();
@@ skipping 666 matching lines @@
 
   scoped_ptr<InstantController> instant_;
   scoped_ptr<InstantUnloadHandler> instant_unload_handler_;
 
   BookmarkBar::State bookmark_bar_state_;
 
   DISALLOW_COPY_AND_ASSIGN(Browser);
 };
 
 #endif  // CHROME_BROWSER_UI_BROWSER_H_