Make members of Singleton<T> private and only visible to the singleton type.

chrome/browser/gtk/browser_toolbar_gtk.cc

 // Copyright (c) 2010 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/gtk/browser_toolbar_gtk.h"
 
 #include <X11/XF86keysym.h>
 #include <gdk/gdkkeysyms.h>
 #include <gtk/gtk.h>
 
@@ skipping 608 matching lines @@
                            !home_page_is_new_tab_page_.IsManaged());
 }
 
 bool BrowserToolbarGtk::ShouldOnlyShowLocation() const {
   // If we're a popup window, only show the location bar (omnibox).
   return browser_->type() != Browser::TYPE_NORMAL;
 }
 
 gboolean BrowserToolbarGtk::OnWrenchMenuButtonExpose(GtkWidget* sender,
                                                      GdkEventExpose* expose) {
-  if (!Singleton<UpgradeDetector>::get()->notify_upgrade())
+  if (!UpgradeDetector::GetInstance()->notify_upgrade())
     return FALSE;
 
   const SkBitmap& badge =
       *theme_provider_->GetBitmapNamed(IDR_UPDATE_BADGE);
 
   // Draw the chrome app menu icon onto the canvas.
   gfx::CanvasSkiaPaint canvas(expose, false);
   int x_offset = base::i18n::IsRTL() ? 0 :
       sender->allocation.width - badge.width();
   int y_offset = 0;
   canvas.DrawBitmapInt(
       badge,
       sender->allocation.x + x_offset,
       sender->allocation.y + y_offset);
 
   return FALSE;
 }