Move Singleton and related structs to namespace base

chrome/browser/ui/views/app_list/linux/app_list_service_linux.h

 // Copyright 2013 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_VIEWS_APP_LIST_LINUX_APP_LIST_SERVICE_LINUX_H_
 #define CHROME_BROWSER_UI_VIEWS_APP_LIST_LINUX_APP_LIST_SERVICE_LINUX_H_
 
 #include "chrome/browser/ui/app_list/app_list_service_views.h"
 #include "ui/app_list/views/app_list_view_observer.h"
 
+namespace base {
 template <typename T> struct DefaultSingletonTraits;
+}
 
 // AppListServiceLinux manages global resources needed for the app list to
 // operate, and controls when the app list is opened and closed.
 class AppListServiceLinux : public AppListServiceViews,
                             public app_list::AppListViewObserver {
  public:
   ~AppListServiceLinux() override;
 
   static AppListServiceLinux* GetInstance();
 
   // AppListService overrides:
   void CreateShortcut() override;
 
   // app_list::AppListViewObserver overrides:
   void OnActivationChanged(views::Widget* widget, bool active) override;
 
  private:
-  friend struct DefaultSingletonTraits<AppListServiceLinux>;
+  friend struct base::DefaultSingletonTraits<AppListServiceLinux>;
 
   // AppListShowerDelegate overrides:
   void OnViewCreated() override;
   void OnViewBeingDestroyed() override;
   void OnViewDismissed() override;
   void MoveNearCursor(app_list::AppListView* view) override;
 
   AppListServiceLinux();
 
   DISALLOW_COPY_AND_ASSIGN(AppListServiceLinux);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_APP_LIST_LINUX_APP_LIST_SERVICE_LINUX_H_