Move Singleton and related structs to namespace base

ui/base/x/x11_menu_list.cc

 // Copyright (c) 2014 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 "ui/base/x/x11_menu_list.h"
 
 #include "base/memory/singleton.h"
 #include "ui/base/x/x11_util.h"
 
 namespace ui {
 
 // static
 XMenuList* XMenuList::GetInstance() {
-  return Singleton<XMenuList>::get();
+  return base::Singleton<XMenuList>::get();
 }
 
 XMenuList::XMenuList()
     : menu_type_atom_(GetAtom("_NET_WM_WINDOW_TYPE_MENU")) {
 }
 
 XMenuList::~XMenuList() {
   menus_.clear();
 }
 
@@ skipping 12 matching lines @@
   if (iter == menus_.end())
     return;
   menus_.erase(iter);
 }
 
 void XMenuList::InsertMenuWindowXIDs(std::vector<XID>* stack) {
   stack->insert(stack->begin(), menus_.begin(), menus_.end());
 }
 
 }  // namespace ui