Move Singleton and related structs to namespace base

chrome/browser/upgrade_detector_impl.h

Index: chrome/browser/upgrade_detector_impl.h
diff --git a/chrome/browser/upgrade_detector_impl.h b/chrome/browser/upgrade_detector_impl.h
index aeba643e5533be724362e642b7bb0ea2fd73ee1c..4cb00cca9722bc67f7fec4d16e63d2ce71a31690 100644
--- a/chrome/browser/upgrade_detector_impl.h
+++ b/chrome/browser/upgrade_detector_impl.h
@@ -11,7 +11,9 @@
 #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,
@@ -38,7 +40,7 @@ class UpgradeDetectorImpl :
   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();