Move Singleton and related structs to namespace base

chrome/browser/ui/app_list/app_list_service_cocoa_mac.h

 // Copyright 2015 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_APP_LIST_APP_LIST_SERVICE_COCOA_MAC_H_
 #define CHROME_BROWSER_UI_APP_LIST_APP_LIST_SERVICE_COCOA_MAC_H_
 
 #include "chrome/browser/ui/app_list/app_list_service_mac.h"
 
 namespace test {
 class AppListServiceMacTestApi;
 }
 
 class AppListControllerDelegateImpl;
 @class AppListWindowController;
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}  // namespace base
 
 // AppListServiceCocoaMac shows and hides the Cocoa app list on Mac.
 class AppListServiceCocoaMac : public AppListServiceMac {
  public:
   ~AppListServiceCocoaMac() override;
 
   static AppListServiceCocoaMac* GetInstance();
 
   // AppListService overrides:
   void ShowForProfile(Profile* requested_profile) override;
   Profile* GetCurrentAppListProfile() override;
   AppListControllerDelegate* GetControllerDelegate() override;
 
   // AppListServiceImpl overrides:
   void CreateForProfile(Profile* requested_profile) override;
   void DestroyAppList() override;
 
  protected:
   // AppListServiceMac overrides:
   NSWindow* GetNativeWindow() const override;
   bool ReadyToShow() override;
 
  private:
   friend class test::AppListServiceMacTestApi;
-  friend struct DefaultSingletonTraits<AppListServiceCocoaMac>;
+  friend struct base::DefaultSingletonTraits<AppListServiceCocoaMac>;
 
   AppListServiceCocoaMac();
 
   Profile* profile_;
   base::scoped_nsobject<AppListWindowController> window_controller_;
   scoped_ptr<AppListControllerDelegateImpl> controller_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListServiceCocoaMac);
 };
 
 #endif  // CHROME_BROWSER_UI_APP_LIST_APP_LIST_SERVICE_COCOA_MAC_H_