Move Singleton and related structs to namespace base

ui/accessibility/platform/atk_util_auralinux.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 UI_ACCESSIBILITY_AX_UTIL_AURALINUX_H_
 #define UI_ACCESSIBILITY_AX_UTIL_AURALINUX_H_
 
 #include "base/memory/singleton.h"
 #include "ui/accessibility/ax_export.h"
 
@@ skipping 10 matching lines @@
  public:
   // Get the single instance of this class.
   static AtkUtilAuraLinux* GetInstance();
 
   AtkUtilAuraLinux();
   virtual ~AtkUtilAuraLinux();
 
   void Initialize(scoped_refptr<base::TaskRunner> init_task_runner);
 
  private:
-  friend struct DefaultSingletonTraits<AtkUtilAuraLinux>;
+  friend struct base::DefaultSingletonTraits<AtkUtilAuraLinux>;
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_UTIL_AURALINUX_H_