Move Singleton and related structs to namespace base

chrome/browser/upgrade_detector_impl.h

 // Copyright (c) 2011 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_UPGRADE_DETECTOR_IMPL_H_
 #define CHROME_BROWSER_UPGRADE_DETECTOR_IMPL_H_
 
 #include "base/memory/weak_ptr.h"
 #include "base/timer/timer.h"
 #include "base/version.h"
 #include "chrome/browser/metrics/variations/variations_service.h"
 #include "chrome/browser/upgrade_detector.h"
 
+namespace base {
 template <typename T> struct DefaultSingletonTraits;
+}
 
 class UpgradeDetectorImpl :
     public UpgradeDetector,
     public chrome_variations::VariationsService::Observer {
  public:
   ~UpgradeDetectorImpl() override;
 
   // Returns the currently installed Chrome version, which may be newer than the
   // one currently running. Not supported on Android, iOS or ChromeOS. Must be
   // run on a thread where I/O operations are allowed (e.g. FILE thread).
   static base::Version GetCurrentlyInstalledVersion();
 
   // Returns the singleton instance.
   static UpgradeDetectorImpl* GetInstance();
 
  protected:
   UpgradeDetectorImpl();
 
   // chrome_variations::VariationsService::Observer:
   void OnExperimentChangesDetected(Severity severity) override;
 
   // Trigger an "on upgrade" notification based on the specified |time_passed|
   // interval. Exposed as protected for testing.
   void NotifyOnUpgradeWithTimePassed(base::TimeDelta time_passed);
 
  private:
-  friend struct DefaultSingletonTraits<UpgradeDetectorImpl>;
+  friend struct base::DefaultSingletonTraits<UpgradeDetectorImpl>;
 
   // Start the timer that will call |CheckForUpgrade()|.
   void StartTimerForUpgradeCheck();
 
   // Launches a task on the file thread to check if we have the latest version.
   void CheckForUpgrade();
 
   // Starts the upgrade notification timer that will check periodically whether
   // enough time has elapsed to update the severity (which maps to visual
   // badging) of the notification.
@@ skipping 43 matching lines @@
   // We use this factory to create callback tasks for UpgradeDetected. We pass
   // the task to the actual upgrade detection code, which is in
   // DetectUpgradeTask.
   base::WeakPtrFactory<UpgradeDetectorImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UpgradeDetectorImpl);
 };
 
 
 #endif  // CHROME_BROWSER_UPGRADE_DETECTOR_IMPL_H_