Move Singleton and related structs to namespace base

chrome/browser/media_galleries/gallery_watch_manager.cc

Index: chrome/browser/media_galleries/gallery_watch_manager.cc
diff --git a/chrome/browser/media_galleries/gallery_watch_manager.cc b/chrome/browser/media_galleries/gallery_watch_manager.cc
index 8ca263f2e7c2c56a85da55c7435d3429417bf3b6..0034024df35d3d6b12d6980012f4938bb4be4a08 100644
--- a/chrome/browser/media_galleries/gallery_watch_manager.cc
+++ b/chrome/browser/media_galleries/gallery_watch_manager.cc
@@ -30,11 +30,11 @@ class ShutdownNotifierFactory
     : public BrowserContextKeyedServiceShutdownNotifierFactory {
  public:
   static ShutdownNotifierFactory* GetInstance() {
-    return Singleton<ShutdownNotifierFactory>::get();
+    return base::Singleton<ShutdownNotifierFactory>::get();
   }
 
  private:
-  friend struct DefaultSingletonTraits<ShutdownNotifierFactory>;
+  friend struct base::DefaultSingletonTraits<ShutdownNotifierFactory>;
 
   ShutdownNotifierFactory()
       : BrowserContextKeyedServiceShutdownNotifierFactory(