Move Singleton and related structs to namespace base

ui/events/gesture_detection/gesture_configuration_default.cc

 // Copyright 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/events/gesture_detection/gesture_configuration.h"
 
 #include "base/memory/singleton.h"
 #include "ui/gfx/screen.h"
 
 namespace ui {
 namespace {
 class GestureConfigurationDefault : public GestureConfiguration {
  public:
   ~GestureConfigurationDefault() override {
   }
 
   static GestureConfigurationDefault* GetInstance() {
-    return Singleton<GestureConfigurationDefault>::get();
+    return base::Singleton<GestureConfigurationDefault>::get();
   }
 
  private:
   GestureConfigurationDefault() {}
 
-  friend struct DefaultSingletonTraits<GestureConfigurationDefault>;
+  friend struct base::DefaultSingletonTraits<GestureConfigurationDefault>;
   DISALLOW_COPY_AND_ASSIGN(GestureConfigurationDefault);
 };
 
 }  // namespace
 
 // Create a GestureConfiguration singleton instance when using Mac.
 GestureConfiguration* GestureConfiguration::GetPlatformSpecificInstance() {
   return GestureConfigurationDefault::GetInstance();
 }
 
 }  // namespace ui